Add workaround for Mac stencil buffer leak

gpu/command_buffer/common/capabilities.h

 // Copyright 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.
 
 #ifndef GPU_COMMAND_BUFFER_COMMON_CAPABILITIES_H_
 #define GPU_COMMAND_BUFFER_COMMON_CAPABILITIES_H_
 
 #include <stdint.h>
 
 #include "gpu/gpu_export.h"
@@ skipping 136 matching lines @@
   bool occlusion_query = false;
   bool occlusion_query_boolean = false;
   bool timer_queries = false;
   bool surfaceless = false;
   bool flips_vertically = false;
   bool msaa_is_slow = false;
   bool disable_one_component_textures = false;
   bool disable_multisampling_color_mask_usage = false;
   bool disable_webgl_rgb_multisampling_usage = false;
   bool gpu_rasterization = false;
+  bool avoid_stencil_buffers = false;
   // True if DirectComposition layers are enabled.
   bool dc_layers = false;
 
   // When this parameter is true, a CHROMIUM image created with RGB format will
   // actually have RGBA format. The client is responsible for handling most of
   // the complexities associated with this. See
   // gpu/GLES2/extensions/CHROMIUM/CHROMIUM_image.txt for more
   // details.
   bool chromium_image_rgb_emulation = false;
 
   // When true, RGB framebuffer formats are unsupported. Emulate with RGBA to
   // work around this. See https://crbug.com/449150 for an example.
   bool emulate_rgb_buffer_with_rgba = false;
 
   // When true, is safe to convert a canvas from software to accelerated.
   // See https://crbug.com/710029.
   bool software_to_accelerated_canvas_upgrade = true;
 
   // When true, non-empty post sub buffer calls are unsupported.
   bool disable_non_empty_post_sub_buffers = false;
 
   int major_version = 2;
   int minor_version = 0;
 };
 
 }  // namespace gpu
 
 #endif  // GPU_COMMAND_BUFFER_COMMON_CAPABILITIES_H_