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diff --git a/devtools/client/shared/vendor/source-map/lib/base64-vlq.js b/devtools/client/shared/vendor/source-map/lib/base64-vlq.js
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+++ b/devtools/client/shared/vendor/source-map/lib/base64-vlq.js
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+/* -*- Mode: js; js-indent-level: 2; -*- */
+/*
+ * Copyright 2011 Mozilla Foundation and contributors
+ * Licensed under the New BSD license. See LICENSE or:
+ * http://opensource.org/licenses/BSD-3-Clause
+ *
+ * Based on the Base 64 VLQ implementation in Closure Compiler:
+ * https://code.google.com/p/closure-compiler/source/browse/trunk/src/com/google/debugging/sourcemap/Base64VLQ.java
+ *
+ * Copyright 2011 The Closure Compiler Authors. All rights reserved.
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above
+ *    copyright notice, this list of conditions and the following
+ *    disclaimer in the documentation and/or other materials provided
+ *    with the distribution.
+ *  * Neither the name of Google Inc. nor the names of its
+ *    contributors may be used to endorse or promote products derived
+ *    from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+const base64 = require("./base64");
+
+// A single base 64 digit can contain 6 bits of data. For the base 64 variable
+// length quantities we use in the source map spec, the first bit is the sign,
+// the next four bits are the actual value, and the 6th bit is the
+// continuation bit. The continuation bit tells us whether there are more
+// digits in this value following this digit.
+//
+//   Continuation
+//   |    Sign
+//   |    |
+//   V    V
+//   101011
+
+const VLQ_BASE_SHIFT = 5;
+
+// binary: 100000
+const VLQ_BASE = 1 << VLQ_BASE_SHIFT;
+
+// binary: 011111
+const VLQ_BASE_MASK = VLQ_BASE - 1;
+
+// binary: 100000
+const VLQ_CONTINUATION_BIT = VLQ_BASE;
+
+/**
+ * Converts from a two-complement value to a value where the sign bit is
+ * placed in the least significant bit.  For example, as decimals:
+ *   1 becomes 2 (10 binary), -1 becomes 3 (11 binary)
+ *   2 becomes 4 (100 binary), -2 becomes 5 (101 binary)
+ */
+function toVLQSigned(aValue) {
+  return aValue < 0 ? (-aValue << 1) + 1 : (aValue << 1) + 0;
+}
+
+/**
+ * Returns the base 64 VLQ encoded value.
+ */
+exports.encode = function base64VLQ_encode(aValue) {
+  let encoded = "";
+  let digit;
+
+  let vlq = toVLQSigned(aValue);
+
+  do {
+    digit = vlq & VLQ_BASE_MASK;
+    vlq >>>= VLQ_BASE_SHIFT;
+    if (vlq > 0) {
+      // There are still more digits in this value, so we must make sure the
+      // continuation bit is marked.
+      digit |= VLQ_CONTINUATION_BIT;
+    }
+    encoded += base64.encode(digit);
+  } while (vlq > 0);
+
+  return encoded;
+};