Android: Set browser offscreen ctx type for stats

TBR=jdduke@chromium.org

Review URL: https://codereview.chromium.org/1155553005

Cr-Commit-Position: refs/heads/master@{#333133}

content/browser/renderer_host/render_widget_host_view_android.cc

@@ -211,6 +211,7 @@ GLHelperHolder::CreateContext3D() {
           0,  // offscreen
           url, gpu_channel_host.get(), attrs, lose_context_when_out_of_memory,
           limits, nullptr));
+  context->SetContextType(BROWSER_OFFSCREEN_MAINTHREAD_CONTEXT);
   if (context->InitializeOnCurrentThread()) {
     context->traceBeginCHROMIUM(
         "gpu_toplevel",