gpu: Add callback for yielding command buffer execution.

gpu/command_buffer/service/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.
 
 import("//build/config/ui.gni")
 import("//third_party/protobuf/proto_library.gni")
 
 group("service") {
   if (is_component_build) {
     public_deps = [
@@ skipping 93 matching lines @@
     "mailbox_manager.cc",
     "mailbox_manager.h",
     "mailbox_manager_impl.cc",
     "mailbox_manager_impl.h",
     "mailbox_manager_sync.cc",
     "mailbox_manager_sync.h",
     "memory_program_cache.cc",
     "memory_program_cache.h",
     "path_manager.cc",
     "path_manager.h",
+    "preemption_flag.h",
     "program_cache.cc",
     "program_cache.h",
     "program_manager.cc",
     "program_manager.h",
     "query_manager.cc",
     "query_manager.h",
     "renderbuffer_manager.cc",
     "renderbuffer_manager.h",
     "sampler_manager.cc",
     "sampler_manager.h",
@@ skipping 69 matching lines @@
     configs -= [ "//build/config/compiler:default_optimization" ]
     configs += [ "//build/config/compiler:optimize_max" ]
   }
 }
 
 proto_library("disk_cache_proto") {
   sources = [
     "disk_cache_proto.proto",
   ]
 }