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diff --git a/third_party/libwebrtc/build/gn_helpers.py b/third_party/libwebrtc/build/gn_helpers.py
new file mode 100644
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+++ b/third_party/libwebrtc/build/gn_helpers.py
@@ -0,0 +1,542 @@
+# Copyright 2014 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+"""Helper functions useful when writing scripts that integrate with GN.
+
+The main functions are ToGNString() and FromGNString(), to convert between
+serialized GN veriables and Python variables.
+
+To use in an arbitrary Python file in the build:
+
+  import os
+  import sys
+
+  sys.path.append(os.path.join(os.path.dirname(__file__),
+                               os.pardir, os.pardir, 'build'))
+  import gn_helpers
+
+Where the sequence of parameters to join is the relative path from your source
+file to the build directory.
+"""
+
+import json
+import os
+import re
+import sys
+
+
+_CHROMIUM_ROOT = os.path.join(os.path.dirname(__file__), os.pardir)
+
+BUILD_VARS_FILENAME = 'build_vars.json'
+IMPORT_RE = re.compile(r'^import\("//(\S+)"\)')
+
+
+class GNError(Exception):
+  pass
+
+
+# Computes ASCII code of an element of encoded Python 2 str / Python 3 bytes.
+_Ord = ord if sys.version_info.major < 3 else lambda c: c
+
+
+def _TranslateToGnChars(s):
+  for decoded_ch in s.encode('utf-8'):  # str in Python 2, bytes in Python 3.
+    code = _Ord(decoded_ch)  # int
+    if code in (34, 36, 92):  # For '"', '$', or '\\'.
+      yield '\\' + chr(code)
+    elif 32 <= code < 127:
+      yield chr(code)
+    else:
+      yield '$0x%02X' % code
+
+
+def ToGNString(value, pretty=False):
+  """Returns a stringified GN equivalent of a Python value.
+
+  Args:
+    value: The Python value to convert.
+    pretty: Whether to pretty print. If true, then non-empty lists are rendered
+        recursively with one item per line, with indents. Otherwise lists are
+        rendered without new line.
+  Returns:
+    The stringified GN equivalent to |value|.
+
+  Raises:
+    GNError: |value| cannot be printed to GN.
+  """
+
+  if sys.version_info.major < 3:
+    basestring_compat = basestring
+  else:
+    basestring_compat = str
+
+  # Emits all output tokens without intervening whitespaces.
+  def GenerateTokens(v, level):
+    if isinstance(v, basestring_compat):
+      yield '"' + ''.join(_TranslateToGnChars(v)) + '"'
+
+    elif isinstance(v, bool):
+      yield 'true' if v else 'false'
+
+    elif isinstance(v, int):
+      yield str(v)
+
+    elif isinstance(v, list):
+      yield '['
+      for i, item in enumerate(v):
+        if i > 0:
+          yield ','
+        for tok in GenerateTokens(item, level + 1):
+          yield tok
+      yield ']'
+
+    elif isinstance(v, dict):
+      if level > 0:
+        yield '{'
+      for key in sorted(v):
+        if not isinstance(key, basestring_compat):
+          raise GNError('Dictionary key is not a string.')
+        if not key or key[0].isdigit() or not key.replace('_', '').isalnum():
+          raise GNError('Dictionary key is not a valid GN identifier.')
+        yield key  # No quotations.
+        yield '='
+        for tok in GenerateTokens(v[key], level + 1):
+          yield tok
+      if level > 0:
+        yield '}'
+
+    else:  # Not supporting float: Add only when needed.
+      raise GNError('Unsupported type when printing to GN.')
+
+  can_start = lambda tok: tok and tok not in ',}]='
+  can_end = lambda tok: tok and tok not in ',{[='
+
+  # Adds whitespaces, trying to keep everything (except dicts) in 1 line.
+  def PlainGlue(gen):
+    prev_tok = None
+    for i, tok in enumerate(gen):
+      if i > 0:
+        if can_end(prev_tok) and can_start(tok):
+          yield '\n'  # New dict item.
+        elif prev_tok == '[' and tok == ']':
+          yield '  '  # Special case for [].
+        elif tok != ',':
+          yield ' '
+      yield tok
+      prev_tok = tok
+
+  # Adds whitespaces so non-empty lists can span multiple lines, with indent.
+  def PrettyGlue(gen):
+    prev_tok = None
+    level = 0
+    for i, tok in enumerate(gen):
+      if i > 0:
+        if can_end(prev_tok) and can_start(tok):
+          yield '\n' + '  ' * level  # New dict item.
+        elif tok == '=' or prev_tok in '=':
+          yield ' '  # Separator before and after '=', on same line.
+      if tok in ']}':
+        level -= 1
+      # Exclude '[]' and '{}' cases.
+      if int(prev_tok == '[') + int(tok == ']') == 1 or \
+         int(prev_tok == '{') + int(tok == '}') == 1:
+        yield '\n' + '  ' * level
+      yield tok
+      if tok in '[{':
+        level += 1
+      if tok == ',':
+        yield '\n' + '  ' * level
+      prev_tok = tok
+
+  token_gen = GenerateTokens(value, 0)
+  ret = ''.join((PrettyGlue if pretty else PlainGlue)(token_gen))
+  # Add terminating '\n' for dict |value| or multi-line output.
+  if isinstance(value, dict) or '\n' in ret:
+    return ret + '\n'
+  return ret
+
+
+def FromGNString(input_string):
+  """Converts the input string from a GN serialized value to Python values.
+
+  For details on supported types see GNValueParser.Parse() below.
+
+  If your GN script did:
+    something = [ "file1", "file2" ]
+    args = [ "--values=$something" ]
+  The command line would look something like:
+    --values="[ \"file1\", \"file2\" ]"
+  Which when interpreted as a command line gives the value:
+    [ "file1", "file2" ]
+
+  You can parse this into a Python list using GN rules with:
+    input_values = FromGNValues(options.values)
+  Although the Python 'ast' module will parse many forms of such input, it
+  will not handle GN escaping properly, nor GN booleans. You should use this
+  function instead.
+
+
+  A NOTE ON STRING HANDLING:
+
+  If you just pass a string on the command line to your Python script, or use
+  string interpolation on a string variable, the strings will not be quoted:
+    str = "asdf"
+    args = [ str, "--value=$str" ]
+  Will yield the command line:
+    asdf --value=asdf
+  The unquoted asdf string will not be valid input to this function, which
+  accepts only quoted strings like GN scripts. In such cases, you can just use
+  the Python string literal directly.
+
+  The main use cases for this is for other types, in particular lists. When
+  using string interpolation on a list (as in the top example) the embedded
+  strings will be quoted and escaped according to GN rules so the list can be
+  re-parsed to get the same result.
+  """
+  parser = GNValueParser(input_string)
+  return parser.Parse()
+
+
+def FromGNArgs(input_string):
+  """Converts a string with a bunch of gn arg assignments into a Python dict.
+
+  Given a whitespace-separated list of
+
+    <ident> = (integer | string | boolean | <list of the former>)
+
+  gn assignments, this returns a Python dict, i.e.:
+
+    FromGNArgs('foo=true\nbar=1\n') -> { 'foo': True, 'bar': 1 }.
+
+  Only simple types and lists supported; variables, structs, calls
+  and other, more complicated things are not.
+
+  This routine is meant to handle only the simple sorts of values that
+  arise in parsing --args.
+  """
+  parser = GNValueParser(input_string)
+  return parser.ParseArgs()
+
+
+def UnescapeGNString(value):
+  """Given a string with GN escaping, returns the unescaped string.
+
+  Be careful not to feed with input from a Python parsing function like
+  'ast' because it will do Python unescaping, which will be incorrect when
+  fed into the GN unescaper.
+
+  Args:
+    value: Input string to unescape.
+  """
+  result = ''
+  i = 0
+  while i < len(value):
+    if value[i] == '\\':
+      if i < len(value) - 1:
+        next_char = value[i + 1]
+        if next_char in ('$', '"', '\\'):
+          # These are the escaped characters GN supports.
+          result += next_char
+          i += 1
+        else:
+          # Any other backslash is a literal.
+          result += '\\'
+    else:
+      result += value[i]
+    i += 1
+  return result
+
+
+def _IsDigitOrMinus(char):
+  return char in '-0123456789'
+
+
+class GNValueParser(object):
+  """Duplicates GN parsing of values and converts to Python types.
+
+  Normally you would use the wrapper function FromGNValue() below.
+
+  If you expect input as a specific type, you can also call one of the Parse*
+  functions directly. All functions throw GNError on invalid input.
+  """
+
+  def __init__(self, string, checkout_root=_CHROMIUM_ROOT):
+    self.input = string
+    self.cur = 0
+    self.checkout_root = checkout_root
+
+  def IsDone(self):
+    return self.cur == len(self.input)
+
+  def ReplaceImports(self):
+    """Replaces import(...) lines with the contents of the imports.
+
+    Recurses on itself until there are no imports remaining, in the case of
+    nested imports.
+    """
+    lines = self.input.splitlines()
+    if not any(line.startswith('import(') for line in lines):
+      return
+    for line in lines:
+      if not line.startswith('import('):
+        continue
+      regex_match = IMPORT_RE.match(line)
+      if not regex_match:
+        raise GNError('Not a valid import string: %s' % line)
+      import_path = os.path.join(self.checkout_root, regex_match.group(1))
+      with open(import_path) as f:
+        imported_args = f.read()
+      self.input = self.input.replace(line, imported_args)
+    # Call ourselves again if we've just replaced an import() with additional
+    # imports.
+    self.ReplaceImports()
+
+
+  def _ConsumeWhitespace(self):
+    while not self.IsDone() and self.input[self.cur] in ' \t\n':
+      self.cur += 1
+
+  def ConsumeCommentAndWhitespace(self):
+    self._ConsumeWhitespace()
+
+    # Consume each comment, line by line.
+    while not self.IsDone() and self.input[self.cur] == '#':
+      # Consume the rest of the comment, up until the end of the line.
+      while not self.IsDone() and self.input[self.cur] != '\n':
+        self.cur += 1
+      # Move the cursor to the next line (if there is one).
+      if not self.IsDone():
+        self.cur += 1
+
+      self._ConsumeWhitespace()
+
+  def Parse(self):
+    """Converts a string representing a printed GN value to the Python type.
+
+    See additional usage notes on FromGNString() above.
+
+    * GN booleans ('true', 'false') will be converted to Python booleans.
+
+    * GN numbers ('123') will be converted to Python numbers.
+
+    * GN strings (double-quoted as in '"asdf"') will be converted to Python
+      strings with GN escaping rules. GN string interpolation (embedded
+      variables preceded by $) are not supported and will be returned as
+      literals.
+
+    * GN lists ('[1, "asdf", 3]') will be converted to Python lists.
+
+    * GN scopes ('{ ... }') are not supported.
+
+    Raises:
+      GNError: Parse fails.
+    """
+    result = self._ParseAllowTrailing()
+    self.ConsumeCommentAndWhitespace()
+    if not self.IsDone():
+      raise GNError("Trailing input after parsing:\n  " + self.input[self.cur:])
+    return result
+
+  def ParseArgs(self):
+    """Converts a whitespace-separated list of ident=literals to a dict.
+
+    See additional usage notes on FromGNArgs(), above.
+
+    Raises:
+      GNError: Parse fails.
+    """
+    d = {}
+
+    self.ReplaceImports()
+    self.ConsumeCommentAndWhitespace()
+
+    while not self.IsDone():
+      ident = self._ParseIdent()
+      self.ConsumeCommentAndWhitespace()
+      if self.input[self.cur] != '=':
+        raise GNError("Unexpected token: " + self.input[self.cur:])
+      self.cur += 1
+      self.ConsumeCommentAndWhitespace()
+      val = self._ParseAllowTrailing()
+      self.ConsumeCommentAndWhitespace()
+      d[ident] = val
+
+    return d
+
+  def _ParseAllowTrailing(self):
+    """Internal version of Parse() that doesn't check for trailing stuff."""
+    self.ConsumeCommentAndWhitespace()
+    if self.IsDone():
+      raise GNError("Expected input to parse.")
+
+    next_char = self.input[self.cur]
+    if next_char == '[':
+      return self.ParseList()
+    elif next_char == '{':
+      return self.ParseScope()
+    elif _IsDigitOrMinus(next_char):
+      return self.ParseNumber()
+    elif next_char == '"':
+      return self.ParseString()
+    elif self._ConstantFollows('true'):
+      return True
+    elif self._ConstantFollows('false'):
+      return False
+    else:
+      raise GNError("Unexpected token: " + self.input[self.cur:])
+
+  def _ParseIdent(self):
+    ident = ''
+
+    next_char = self.input[self.cur]
+    if not next_char.isalpha() and not next_char=='_':
+      raise GNError("Expected an identifier: " + self.input[self.cur:])
+
+    ident += next_char
+    self.cur += 1
+
+    next_char = self.input[self.cur]
+    while next_char.isalpha() or next_char.isdigit() or next_char=='_':
+      ident += next_char
+      self.cur += 1
+      next_char = self.input[self.cur]
+
+    return ident
+
+  def ParseNumber(self):
+    self.ConsumeCommentAndWhitespace()
+    if self.IsDone():
+      raise GNError('Expected number but got nothing.')
+
+    begin = self.cur
+
+    # The first character can include a negative sign.
+    if not self.IsDone() and _IsDigitOrMinus(self.input[self.cur]):
+      self.cur += 1
+    while not self.IsDone() and self.input[self.cur].isdigit():
+      self.cur += 1
+
+    number_string = self.input[begin:self.cur]
+    if not len(number_string) or number_string == '-':
+      raise GNError('Not a valid number.')
+    return int(number_string)
+
+  def ParseString(self):
+    self.ConsumeCommentAndWhitespace()
+    if self.IsDone():
+      raise GNError('Expected string but got nothing.')
+
+    if self.input[self.cur] != '"':
+      raise GNError('Expected string beginning in a " but got:\n  ' +
+                    self.input[self.cur:])
+    self.cur += 1  # Skip over quote.
+
+    begin = self.cur
+    while not self.IsDone() and self.input[self.cur] != '"':
+      if self.input[self.cur] == '\\':
+        self.cur += 1  # Skip over the backslash.
+        if self.IsDone():
+          raise GNError('String ends in a backslash in:\n  ' + self.input)
+      self.cur += 1
+
+    if self.IsDone():
+      raise GNError('Unterminated string:\n  ' + self.input[begin:])
+
+    end = self.cur
+    self.cur += 1  # Consume trailing ".
+
+    return UnescapeGNString(self.input[begin:end])
+
+  def ParseList(self):
+    self.ConsumeCommentAndWhitespace()
+    if self.IsDone():
+      raise GNError('Expected list but got nothing.')
+
+    # Skip over opening '['.
+    if self.input[self.cur] != '[':
+      raise GNError('Expected [ for list but got:\n  ' + self.input[self.cur:])
+    self.cur += 1
+    self.ConsumeCommentAndWhitespace()
+    if self.IsDone():
+      raise GNError('Unterminated list:\n  ' + self.input)
+
+    list_result = []
+    previous_had_trailing_comma = True
+    while not self.IsDone():
+      if self.input[self.cur] == ']':
+        self.cur += 1  # Skip over ']'.
+        return list_result
+
+      if not previous_had_trailing_comma:
+        raise GNError('List items not separated by comma.')
+
+      list_result += [ self._ParseAllowTrailing() ]
+      self.ConsumeCommentAndWhitespace()
+      if self.IsDone():
+        break
+
+      # Consume comma if there is one.
+      previous_had_trailing_comma = self.input[self.cur] == ','
+      if previous_had_trailing_comma:
+        # Consume comma.
+        self.cur += 1
+        self.ConsumeCommentAndWhitespace()
+
+    raise GNError('Unterminated list:\n  ' + self.input)
+
+  def ParseScope(self):
+    self.ConsumeCommentAndWhitespace()
+    if self.IsDone():
+      raise GNError('Expected scope but got nothing.')
+
+    # Skip over opening '{'.
+    if self.input[self.cur] != '{':
+      raise GNError('Expected { for scope but got:\n ' + self.input[self.cur:])
+    self.cur += 1
+    self.ConsumeCommentAndWhitespace()
+    if self.IsDone():
+      raise GNError('Unterminated scope:\n ' + self.input)
+
+    scope_result = {}
+    while not self.IsDone():
+      if self.input[self.cur] == '}':
+        self.cur += 1
+        return scope_result
+
+      ident = self._ParseIdent()
+      self.ConsumeCommentAndWhitespace()
+      if self.input[self.cur] != '=':
+        raise GNError("Unexpected token: " + self.input[self.cur:])
+      self.cur += 1
+      self.ConsumeCommentAndWhitespace()
+      val = self._ParseAllowTrailing()
+      self.ConsumeCommentAndWhitespace()
+      scope_result[ident] = val
+
+    raise GNError('Unterminated scope:\n ' + self.input)
+
+  def _ConstantFollows(self, constant):
+    """Checks and maybe consumes a string constant at current input location.
+
+    Param:
+      constant: The string constant to check.
+
+    Returns:
+      True if |constant| follows immediately at the current location in the
+      input. In this case, the string is consumed as a side effect. Otherwise,
+      returns False and the current position is unchanged.
+    """
+    end = self.cur + len(constant)
+    if end > len(self.input):
+      return False  # Not enough room.
+    if self.input[self.cur:end] == constant:
+      self.cur = end
+      return True
+    return False
+
+
+def ReadBuildVars(output_directory):
+  """Parses $output_directory/build_vars.json into a dict."""
+  with open(os.path.join(output_directory, BUILD_VARS_FILENAME)) as f:
+    return json.load(f)