Add a |scope| argument to TRACE_EVENT_INSTANT* and require its presence.

content/common/gpu/image_transport_surface.cc

Index: content/common/gpu/image_transport_surface.cc
diff --git a/content/common/gpu/image_transport_surface.cc b/content/common/gpu/image_transport_surface.cc
index 460c20a989a2701938bdc5a1ef44baa88e3cce46..1f904d0b9ff1b10fbe3da20403040d6f9b39086e 100644
--- a/content/common/gpu/image_transport_surface.cc
+++ b/content/common/gpu/image_transport_surface.cc
@@ -68,6 +68,7 @@ void ImageTransportHelper::SendAcceleratedSurfaceBuffersSwapped(
     GpuHostMsg_AcceleratedSurfaceBuffersSwapped_Params params) {
   // TRACE_EVENT for gpu tests:
   TRACE_EVENT_INSTANT2("test_gpu", "SwapBuffers",
+                       TRACE_EVENT_SCOPE_THREAD,
                        "GLImpl", static_cast<int>(gfx::GetGLImplementation()),
                        "width", params.size.width());
   params.surface_id = stub_->surface_id();