Add exceptions to features in GpuControlList

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 34 matching lines @@
 // 13. "gl_renderer" is a string pattern.
 // 14. "gl_extensions" is a string pattern.
 // 15. "machine_model_name" is an array of string patterns.
 // 16. "machine_model_version" is a VERSION structure (defined below).
 // 17. "gpu_count" is a INT structure (defined below).
 // 18. "cpu_info" is a string pattern.
 // 19. "exceptions" is a list of entries.
 // 20. "features" is a list of gpu control list options, which can be
 //     configured by a specific list. See its *_json.cc file for a list of
 //     supported features. This field is mandatory.
+//     An "exceptions" list to the features can be added for convenience instead
+//     of listing all features except one.
 // 21. "description" has the description of the entry.
 // 22. "webkit_bugs" is an array of associated webkit bug numbers.
 // 23. "cr_bugs" is an array of associated webkit bug numbers.
 // 24. "disabled" is a boolean. If it is present, the entry will be skipped.
 //     This can not be used in exceptions.
 // 25. "direct_rendering" is a boolean. If present, this will filter on whether
 //     the GL contexts are direct or indirect based on the value.
 // 26. "disabled_extensions" is a list of strings which contain the GL_EXTENSION
 //     strings which are disabled by the workaround.
 //
 // VERSION includes "op", "style", "value", and "value2".  "op" can be any of
 // the following values: "=", "<", "<=", ">", ">=", "any", "between".  "style"
 // is optional and can be "lexical" or "numerical"; if it's not specified, it
 // defaults to "numerical".  "value2" is only used if "op" is "between".
 // "between" is "value <= * <= value2".
 // "value" is used for all "op" values except "any". "value" and "value2"
 // are in the format of x, x.x, x.x.x, etc.
 // Only "driver_version" supports lexical style if the format is major.minor;
 // 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://github.com/google/re2/blob/master/doc/syntax.txt