Revert workaround due to perf regression

content/public/common/web_preferences.h

 // 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.
 
 #ifndef CONTENT_PUBLIC_COMMON_WEB_PREFERENCES_H_
 #define CONTENT_PUBLIC_COMMON_WEB_PREFERENCES_H_
 
 #include <map>
 #include <string>
 #include <vector>
@@ skipping 116 matching lines @@
   bool privileged_webgl_extensions_enabled;
   bool webgl_errors_to_console_enabled;
   bool mock_scrollbars_enabled;
   bool hide_scrollbars;
   bool accelerated_2d_canvas_enabled;
   int minimum_accelerated_2d_canvas_size;
   bool disable_2d_canvas_copy_on_write;
   bool antialiased_2d_canvas_disabled;
   bool antialiased_clips_2d_canvas_enabled;
   int accelerated_2d_canvas_msaa_sample_count;
-  bool force_software_readback_from_2d_canvas;
   bool accelerated_filters_enabled;
   bool deferred_filters_enabled;
   bool container_culling_enabled;
   bool allow_running_insecure_content;
   // If true, taints all <canvas> elements, regardless of origin.
   bool disable_reading_from_canvas;
   // Strict mixed content checking disables both displaying and running insecure
   // mixed content, and disables embedder notifications that such content was
   // requested (thereby preventing user override).
   bool strict_mixed_content_checking;
@@ skipping 118 matching lines @@
   // chrome, except for the cases where it would require lots of extra work for
   // the embedder to use the same default value.
   WebPreferences();
   WebPreferences(const WebPreferences& other);
   ~WebPreferences();
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_COMMON_WEB_PREFERENCES_H_