Fix Windows build warning LNK4217 for blink_platform.dll.

gpu/ipc/common/BUILD.gn

 # Copyright 2016 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("//mojo/public/tools/bindings/mojom.gni")
 
 group("common") {
   if (is_component_build) {
     public_deps = [
@@ skipping 133 matching lines @@
     "mailbox.mojom",
     "mailbox_holder.mojom",
     "surface_handle.mojom",
     "sync_token.mojom",
   ]
 
   public_deps = [
     "//mojo/common:common_custom_types",
     "//ui/gfx/geometry/mojo",
   ]
+
+  export_class_attribute_blink = "BLINK_PLATFORM_EXPORT"
+  export_define_blink = "BLINK_PLATFORM_IMPLEMENTATION=1"
+  export_header_blink = "third_party/WebKit/public/platform/WebCommon.h"
 }
 
 mojom("test_interfaces") {
   testonly = true
   sources = [
     "traits_test_service.mojom",
   ]
 
   public_deps = [
     ":interfaces",
   ]
 }
 
 source_set("struct_traits") {
   sources = [
     "mailbox_holder_struct_traits.h",
     "mailbox_struct_traits.h",
     "surface_handle_struct_traits.h",
     "sync_token_struct_traits.h",
   ]
   deps = [
     ":interfaces_shared_cpp_sources",
     ":surface_handle_type",
     "//gpu/command_buffer/common",
     "//mojo/public/cpp/bindings:bindings",
   ]
 }