gpu: Fix some context lost marking glitches+leaks and add UMA stats

gpu/BUILD.gn

 # 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.
 
 # GYP-to-GN project mappings:
 #
 #  gpu.gyp:command_buffer_client => //gpu/command_buffer/client
 #
 #  gpu.gyp:command_buffer_common => //gpu/command_buffer/common
 #
@@ skipping 149 matching lines @@
     "command_buffer/service/async_pixel_transfer_delegate_mock.h",
     "command_buffer/service/async_pixel_transfer_manager_mock.cc",
     "command_buffer/service/async_pixel_transfer_manager_mock.h",
     "command_buffer/service/buffer_manager_unittest.cc",
     "command_buffer/service/cmd_parser_test.cc",
     "command_buffer/service/command_buffer_service_unittest.cc",
     "command_buffer/service/common_decoder_unittest.cc",
     "command_buffer/service/context_group_unittest.cc",
     "command_buffer/service/feature_info_unittest.cc",
     "command_buffer/service/framebuffer_manager_unittest.cc",
+    "command_buffer/service/gl_context_mock.cc",
+    "command_buffer/service/gl_context_mock.h",
     "command_buffer/service/gl_surface_mock.cc",
     "command_buffer/service/gl_surface_mock.h",
     "command_buffer/service/gles2_cmd_decoder_unittest.cc",
     "command_buffer/service/gles2_cmd_decoder_unittest.h",
     "command_buffer/service/gles2_cmd_decoder_unittest_0_autogen.h",
     "command_buffer/service/gles2_cmd_decoder_unittest_1.cc",
     "command_buffer/service/gles2_cmd_decoder_unittest_1_autogen.h",
     "command_buffer/service/gles2_cmd_decoder_unittest_2.cc",
     "command_buffer/service/gles2_cmd_decoder_unittest_2_autogen.h",
     "command_buffer/service/gles2_cmd_decoder_unittest_3.cc",
     "command_buffer/service/gles2_cmd_decoder_unittest_3_autogen.h",
     "command_buffer/service/gles2_cmd_decoder_unittest_async_pixel.cc",
     "command_buffer/service/gles2_cmd_decoder_unittest_attribs.cc",
     "command_buffer/service/gles2_cmd_decoder_unittest_base.cc",
     "command_buffer/service/gles2_cmd_decoder_unittest_base.h",
     "command_buffer/service/gles2_cmd_decoder_unittest_buffers.cc",
+    "command_buffer/service/gles2_cmd_decoder_unittest_context_lost.cc",
     "command_buffer/service/gles2_cmd_decoder_unittest_context_state.cc",
     "command_buffer/service/gles2_cmd_decoder_unittest_drawing.cc",
     "command_buffer/service/gles2_cmd_decoder_unittest_extensions.cc",
     "command_buffer/service/gles2_cmd_decoder_unittest_framebuffers.cc",
     "command_buffer/service/gles2_cmd_decoder_unittest_programs.cc",
     "command_buffer/service/gles2_cmd_decoder_unittest_textures.cc",
     "command_buffer/service/gles2_cmd_decoder_unittest_valuebuffer.cc",
     "command_buffer/service/gpu_scheduler_unittest.cc",
     "command_buffer/service/gpu_service_test.cc",
     "command_buffer/service/gpu_service_test.h",
@@ skipping 78 matching lines @@
 
   deps = [
     "//base",
     "//base/test:test_support",
     "//base/third_party/dynamic_annotations",
     "//testing/gmock",
     "//testing/gtest",
     "//third_party/angle:translator_static",
   ]
 }