aw: Make DrawFunctor event toplevel

Bug: 812955
Change-Id: Ice08cc78a2b3f2849d6fdcb1ce4c0e191088fd79
Reviewed-on: https://chromium-review.googlesource.com/923392Reviewed-by: Victor Miura <vmiura@chromium.org>
Commit-Queue: Victor Miura <vmiura@chromium.org>
Cr-Commit-Position: refs/heads/master@{#537393}

android_webview/browser/render_thread_manager.cc

@@ -288,7 +288,7 @@ bool RenderThreadManager::ReturnedResourcesEmptyOnUI() const {
 }
 
 void RenderThreadManager::DrawGL(AwDrawGLInfo* draw_info) {
-  TRACE_EVENT0("android_webview", "DrawFunctor");
+  TRACE_EVENT0("android_webview,toplevel", "DrawFunctor");
   if (draw_info->mode == AwDrawGLInfo::kModeSync) {
     TRACE_EVENT_INSTANT0("android_webview", "kModeSync",
                          TRACE_EVENT_SCOPE_THREAD);