Defer compositor context creation to the thread.

content/renderer/gpu/render_widget_compositor_unittest.cc

Index: content/renderer/gpu/render_widget_compositor_unittest.cc
diff --git a/content/renderer/gpu/render_widget_compositor_unittest.cc b/content/renderer/gpu/render_widget_compositor_unittest.cc
index 11c3a575a4c51a6c2ce3efd4e8af34a30f26ccb7..c184c342beba43f6d7acea1bc87be3a70c34598f 100644
--- a/content/renderer/gpu/render_widget_compositor_unittest.cc
+++ b/content/renderer/gpu/render_widget_compositor_unittest.cc
@@ -148,8 +148,6 @@ class RenderWidgetCompositorOutputSurface : public RenderWidgetCompositor {
     if (success) {
       std::unique_ptr<cc::TestWebGraphicsContext3D> context =
           cc::TestWebGraphicsContext3D::Create();
-      // Image support required for synchronous compositing.
-      context->set_support_image(true);
       // Create delegating surface so that max_pending_frames = 1.
       return cc::FakeOutputSurface::CreateDelegating3d(std::move(context));
     }