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diff --git a/third_party/libwebrtc/tools_webrtc/vim/webrtc.ycm_extra_conf.py b/third_party/libwebrtc/tools_webrtc/vim/webrtc.ycm_extra_conf.py
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+#!/usr/bin/env vpython3
+
+# Copyright (c) 2017 The WebRTC project authors. All Rights Reserved.
+#
+# Use of this source code is governed by a BSD-style license
+# that can be found in the LICENSE file in the root of the source
+# tree. An additional intellectual property rights grant can be found
+# in the file PATENTS.  All contributing project authors may
+# be found in the AUTHORS file in the root of the source tree.
+
+# Autocompletion config for YouCompleteMe in WebRTC. This is just copied from
+# tools/vim in chromium with very minor modifications.
+#
+# USAGE:
+#
+#   1. Install YCM [https://github.com/Valloric/YouCompleteMe]
+#          (Googlers should check out [go/ycm])
+#
+#   2. Create a symbolic link to this file called .ycm_extra_conf.py in the
+#      directory above your WebRTC checkout (i.e. next to your .gclient file).
+#
+#          cd src
+#          ln -rs tools_webrtc/vim/webrtc.ycm_extra_conf.py \
+#          ../.ycm_extra_conf.py
+#
+#   3. (optional) Whitelist the .ycm_extra_conf.py from step #2 by adding the
+#      following to your .vimrc:
+#
+#          let g:ycm_extra_conf_globlist=['<path to .ycm_extra_conf.py>']
+#
+#      You can also add other .ycm_extra_conf.py files you want to use to this
+#      list to prevent excessive prompting each time you visit a directory
+#      covered by a config file.
+#
+#   4. Profit
+#
+#
+# Usage notes:
+#
+#   * You must use ninja & clang to build WebRTC.
+#
+#   * You must have run "gn gen" and built WebRTC recently.
+#
+#
+# Hacking notes:
+#
+#   * The purpose of this script is to construct an accurate enough command line
+#     for YCM to pass to clang so it can build and extract the symbols.
+#
+#   * Right now, we only pull the -I and -D flags. That seems to be sufficient
+#     for everything I've used it for.
+#
+#   * That whole ninja & clang thing? We could support other configs if someone
+#     were willing to write the correct commands and a parser.
+#
+#   * This has only been tested on gPrecise.
+
+import os
+import os.path
+import shlex
+import subprocess
+import sys
+
+# Flags from YCM's default config.
+_DEFAULT_FLAGS = [
+    '-DUSE_CLANG_COMPLETER',
+    '-std=c++11',
+    '-x',
+    'c++',
+]
+
+_HEADER_ALTERNATES = ('.cc', '.cpp', '.c', '.mm', '.m')
+
+_EXTENSION_FLAGS = {
+    '.m': ['-x', 'objective-c'],
+    '.mm': ['-x', 'objective-c++'],
+}
+
+
+def FindWebrtcSrcFromFilename(filename):
+  """Searches for the root of the WebRTC checkout.
+
+  Simply checks parent directories until it finds .gclient and src/.
+
+  Args:
+    filename: (String) Path to source file being edited.
+
+  Returns:
+    (String) Path of 'src/', or None if unable to find.
+  """
+  curdir = os.path.normpath(os.path.dirname(filename))
+  while not (os.path.basename(curdir) == 'src'
+             and os.path.exists(os.path.join(curdir, 'DEPS')) and
+             (os.path.exists(os.path.join(curdir, '..', '.gclient'))
+              or os.path.exists(os.path.join(curdir, '.git')))):
+    nextdir = os.path.normpath(os.path.join(curdir, '..'))
+    if nextdir == curdir:
+      return None
+    curdir = nextdir
+  return curdir
+
+
+def GetDefaultSourceFile(webrtc_root, filename):
+  """Returns the default source file to use as an alternative to `filename`.
+
+  Compile flags used to build the default source file is assumed to be a
+  close-enough approximation for building `filename`.
+
+  Args:
+    webrtc_root: (String) Absolute path to the root of WebRTC checkout.
+    filename: (String) Absolute path to the source file.
+
+  Returns:
+    (String) Absolute path to substitute source file.
+  """
+  if 'test.' in filename:
+    return os.path.join(webrtc_root, 'base', 'logging_unittest.cc')
+  return os.path.join(webrtc_root, 'base', 'logging.cc')
+
+
+def GetNinjaBuildOutputsForSourceFile(out_dir, filename):
+  """Returns a list of build outputs for filename.
+
+  The list is generated by invoking 'ninja -t query' tool to retrieve a list of
+  inputs and outputs of `filename`. This list is then filtered to only include
+  .o and .obj outputs.
+
+  Args:
+    out_dir: (String) Absolute path to ninja build output directory.
+    filename: (String) Absolute path to source file.
+
+  Returns:
+    (List of Strings) List of target names. Will return [] if `filename` doesn't
+        yield any .o or .obj outputs.
+  """
+  # Ninja needs the path to the source file relative to the output build
+  # directory.
+  rel_filename = os.path.relpath(filename, out_dir)
+
+  p = subprocess.Popen(['ninja', '-C', out_dir, '-t', 'query', rel_filename],
+                       stdout=subprocess.PIPE,
+                       stderr=subprocess.STDOUT,
+                       universal_newlines=True)
+  stdout, _ = p.communicate()
+  if p.returncode != 0:
+    return []
+
+  # The output looks like:
+  #   ../../relative/path/to/source.cc:
+  #     outputs:
+  #       obj/reative/path/to/target.source.o
+  #       obj/some/other/target2.source.o
+  #       another/target.txt
+  #
+  outputs_text = stdout.partition('\n  outputs:\n')[2]
+  output_lines = [line.strip() for line in outputs_text.split('\n')]
+  return [
+      target for target in output_lines
+      if target and (target.endswith('.o') or target.endswith('.obj'))
+  ]
+
+
+def GetClangCommandLineForNinjaOutput(out_dir, build_target):
+  """Returns the Clang command line for building `build_target`
+
+  Asks ninja for the list of commands used to build `filename` and returns the
+  final Clang invocation.
+
+  Args:
+    out_dir: (String) Absolute path to ninja build output directory.
+    build_target: (String) A build target understood by ninja
+
+  Returns:
+    (String or None) Clang command line or None if a Clang command line couldn't
+        be determined.
+  """
+  p = subprocess.Popen(
+      ['ninja', '-v', '-C', out_dir, '-t', 'commands', build_target],
+      stdout=subprocess.PIPE,
+      universal_newlines=True)
+  stdout, _ = p.communicate()
+  if p.returncode != 0:
+    return None
+
+  # Ninja will return multiple build steps for all dependencies up to
+  # `build_target`. The build step we want is the last Clang invocation, which
+  # is expected to be the one that outputs `build_target`.
+  for line in reversed(stdout.split('\n')):
+    if 'clang' in line:
+      return line
+  return None
+
+
+def GetClangCommandLineFromNinjaForSource(out_dir, filename):
+  """Returns a Clang command line used to build `filename`.
+
+  The same source file could be built multiple times using different tool
+  chains. In such cases, this command returns the first Clang invocation. We
+  currently don't prefer one toolchain over another. Hopefully the tool chain
+  corresponding to the Clang command line is compatible with the Clang build
+  used by YCM.
+
+  Args:
+    out_dir: (String) Absolute path to WebRTC checkout.
+    filename: (String) Absolute path to source file.
+
+  Returns:
+    (String or None): Command line for Clang invocation using `filename` as a
+        source. Returns None if no such command line could be found.
+  """
+  build_targets = GetNinjaBuildOutputsForSourceFile(out_dir, filename)
+  for build_target in build_targets:
+    command_line = GetClangCommandLineForNinjaOutput(out_dir, build_target)
+    if command_line:
+      return command_line
+  return None
+
+
+def GetClangOptionsFromCommandLine(clang_commandline, out_dir,
+                                   additional_flags):
+  """Extracts relevant command line options from `clang_commandline`
+
+  Args:
+    clang_commandline: (String) Full Clang invocation.
+    out_dir: (String) Absolute path to ninja build directory. Relative paths in
+        the command line are relative to `out_dir`.
+    additional_flags: (List of String) Additional flags to return.
+
+  Returns:
+    (List of Strings) The list of command line flags for this source file. Can
+    be empty.
+  """
+  clang_flags = [] + additional_flags
+
+  # Parse flags that are important for YCM's purposes.
+  clang_tokens = shlex.split(clang_commandline)
+  for flag_index, flag in enumerate(clang_tokens):
+    if flag.startswith('-I'):
+      # Relative paths need to be resolved, because they're relative to
+      # the output dir, not the source.
+      if flag[2] == '/':
+        clang_flags.append(flag)
+      else:
+        abs_path = os.path.normpath(os.path.join(out_dir, flag[2:]))
+        clang_flags.append('-I' + abs_path)
+    elif flag.startswith('-std'):
+      clang_flags.append(flag)
+    elif flag.startswith('-') and flag[1] in 'DWFfmO':
+      if flag in ['-Wno-deprecated-register', '-Wno-header-guard']:
+        # These flags causes libclang (3.3) to crash. Remove it until
+        # things are fixed.
+        continue
+      clang_flags.append(flag)
+    elif flag == '-isysroot':
+      # On Mac -isysroot <path> is used to find the system headers.
+      # Copy over both flags.
+      if flag_index + 1 < len(clang_tokens):
+        clang_flags.append(flag)
+        clang_flags.append(clang_tokens[flag_index + 1])
+    elif flag.startswith('--sysroot='):
+      # On Linux we use a sysroot image.
+      sysroot_path = flag.lstrip('--sysroot=')
+      if sysroot_path.startswith('/'):
+        clang_flags.append(flag)
+      else:
+        abs_path = os.path.normpath(os.path.join(out_dir, sysroot_path))
+        clang_flags.append('--sysroot=' + abs_path)
+  return clang_flags
+
+
+def GetClangOptionsFromNinjaForFilename(webrtc_root, filename):
+  """Returns the Clang command line options needed for building `filename`.
+
+  Command line options are based on the command used by ninja for building
+  `filename`. If `filename` is a .h file, uses its companion .cc or .cpp file.
+  If a suitable companion file can't be located or if ninja doesn't know about
+  `filename`, then uses default source files in WebRTC for determining the
+  commandline.
+
+  Args:
+    webrtc_root: (String) Path to src/.
+    filename: (String) Absolute path to source file being edited.
+
+  Returns:
+    (List of Strings) The list of command line flags for this source file. Can
+    be empty.
+  """
+  if not webrtc_root:
+    return []
+
+  # Generally, everyone benefits from including WebRTC's src/, because all of
+  # WebRTC's includes are relative to that.
+  additional_flags = ['-I' + os.path.join(webrtc_root)]
+
+  # Version of Clang used to compile WebRTC can be newer then version of
+  # libclang that YCM uses for completion. So it's possible that YCM's
+  # libclang doesn't know about some used warning options, which causes
+  # compilation warnings (and errors, because of '-Werror');
+  additional_flags.append('-Wno-unknown-warning-option')
+
+  sys.path.append(os.path.join(webrtc_root, 'tools', 'vim'))
+  from ninja_output import GetNinjaOutputDirectory
+  out_dir = GetNinjaOutputDirectory(webrtc_root)
+
+  basename, extension = os.path.splitext(filename)
+  if extension == '.h':
+    candidates = [basename + ext for ext in _HEADER_ALTERNATES]
+  else:
+    candidates = [filename]
+
+  clang_line = None
+  buildable_extension = extension
+  for candidate in candidates:
+    clang_line = GetClangCommandLineFromNinjaForSource(out_dir, candidate)
+    if clang_line:
+      buildable_extension = os.path.splitext(candidate)[1]
+      break
+
+  additional_flags += _EXTENSION_FLAGS.get(buildable_extension, [])
+
+  if not clang_line:
+    # If ninja didn't know about filename or it's companion files, then try
+    # a default build target. It is possible that the file is new, or
+    # build.ninja is stale.
+    clang_line = GetClangCommandLineFromNinjaForSource(
+        out_dir, GetDefaultSourceFile(webrtc_root, filename))
+
+  if not clang_line:
+    return additional_flags
+
+  return GetClangOptionsFromCommandLine(clang_line, out_dir, additional_flags)
+
+
+def FlagsForFile(filename):
+  """This is the main entry point for YCM. Its interface is fixed.
+
+  Args:
+    filename: (String) Path to source file being edited.
+
+  Returns:
+    (Dictionary)
+      'flags': (List of Strings) Command line flags.
+      'do_cache': (Boolean) True if the result should be cached.
+  """
+  abs_filename = os.path.abspath(filename)
+  webrtc_root = FindWebrtcSrcFromFilename(abs_filename)
+  clang_flags = GetClangOptionsFromNinjaForFilename(webrtc_root, abs_filename)
+
+  # If clang_flags could not be determined, then assume that was due to a
+  # transient failure. Preventing YCM from caching the flags allows us to
+  # try to determine the flags again.
+  should_cache_flags_for_file = bool(clang_flags)
+
+  final_flags = _DEFAULT_FLAGS + clang_flags
+
+  return {'flags': final_flags, 'do_cache': should_cache_flags_for_file}