Identify the active GPU using GL strings in multiple GPU situation.

gpu/config/gpu_control_list_format.txt

 // Copyright (c) 2013 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.
 
 // A valid gpu control list json file is in the format of
 // {
 //   "version": "x.y",
 //   "entries": [
 //     { // entry 1
 //     },
@@ skipping 12 matching lines @@
 //    "version" is a VERSION structure (defined below).
 // 3. "vendor_id" is a string.  0 is reserved.
 // 4. "device_id" is an array of strings.  0 is reserved.
 // 5. "multi_gpu_style" is a string, valid values include:
 //      a) "optimus": NVIDIA dual GPU
 //      b) "amd_switchable": AMD dual GPU
 //      c) "amd_switchable_integrated": AMD dual GPU, integrated GPU is active
 //      d) "amd_switchable_discrete": AMD dual GPU, discrete GPU is active
 //    c) and d) are only valid on Win, as on Mac we can switch GPU on the fly.
 // 6. "multi_gpu_category" is a string, valid values include "any", "primary",
-//    "secondary", and "active". If unspecified, the default value is "primary".
+//    "secondary", and "active". If unspecified, the default value is "active".
 //    See gpu_control_list.h for more details on the meanings of the strings.
 // 7. "driver_vendor" is a string pattern.
 // 8. "driver_version" is a VERSION structure (defined below).
 // 9. "driver_date" is a VERSION structure (defined below).
 //    The version is interpreted as "year.month.day".
 // 10. "gl_type" is a string, valid values include "gl", "gles", and "angle".
 //    If "gl_version" is specified and "gl_type" is not, use the default value.
 //    The default value on Android is "gles", on Windows is "angle", on other
 //    platforms is "gl".
 // 11. "gl_version" is a VERSION structure (defined below).
@@ skipping 29 matching lines @@
 // in that case, major is still numerical, but minor is lexical. 
 //
 // FLOAT includes "op" "value", and "value2".  "op" can be any of the
 // following values: "=", "<", "<=", ">", ">=", "any", "between".  "value2" is
 // only used if "op" is "between".  "value" is used for all "op" values except
 // "any". "value" and "value2" are valid float numbers.
 // INT is very much like FLOAT, except that the values need to be integers.
 //
 // String pattern syntax can be found at
 // https://code.google.com/p/re2/wiki/Syntax.