Have Blink be told of scrollbar changes rather than paying attention itself (Chromium side).

content/browser/browser_main_loop.cc

 // Copyright (c) 2012 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.
 
 #include "content/browser/browser_main_loop.h"
 
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/debug/trace_event.h"
 #include "base/file_util.h"
@@ skipping 52 matching lines @@
 #if defined(USE_AURA)
 #include "content/browser/aura/image_transport_factory.h"
 #endif
 
 #if defined(OS_ANDROID)
 #include "base/android/jni_android.h"
 #include "content/browser/android/browser_startup_controller.h"
 #include "content/browser/android/surface_texture_peer_browser_impl.h"
 #endif
 
+#if defined(OS_MACOSX)
+#include "content/browser/theme_helper_mac.h"
+#endif
+
 #if defined(OS_WIN)
 #include <windows.h>
 #include <commctrl.h>
 #include <shellapi.h>
 
 #include "base/win/text_services_message_filter.h"
 #include "content/browser/system_message_window_win.h"
 #include "content/common/sandbox_win.h"
 #include "net/base/winsock_init.h"
 #include "ui/base/l10n/l10n_util_win.h"
@@ skipping 931 matching lines @@
       !parsed_command_line_.HasSwitch(switches::kInProcessGPU)) {
     TRACE_EVENT_INSTANT0("gpu", "Post task to launch GPU process",
                          TRACE_EVENT_SCOPE_THREAD);
     BrowserThread::PostTask(
         BrowserThread::IO, FROM_HERE, base::Bind(
             base::IgnoreResult(&GpuProcessHost::Get),
             GpuProcessHost::GPU_PROCESS_KIND_SANDBOXED,
             CAUSE_FOR_GPU_LAUNCH_BROWSER_STARTUP));
   }
 #endif  // !defined(OS_IOS)
+
+#if defined(OS_MACOSX)
+  ThemeHelperMac::GetInstance();
+#endif
   return result_code_;
 }
 
 void BrowserMainLoop::InitializeToolkit() {
   TRACE_EVENT0("startup", "BrowserMainLoop::InitializeToolkit")
   // TODO(evan): this function is rather subtle, due to the variety
   // of intersecting ifdefs we have.  To keep it easy to follow, there
   // are no #else branches on any #ifs.
   // TODO(stevenjb): Move platform specific code into platform specific Parts
   // (Need to add InitializeToolkit stage to BrowserParts).
@@ skipping 27 matching lines @@
   if (parameters_.ui_task)
     base::MessageLoopForUI::current()->PostTask(FROM_HERE,
                                                 *parameters_.ui_task);
 
   base::RunLoop run_loop;
   run_loop.Run();
 #endif
 }
 
 }  // namespace content