Fix bug whereby OnGpuSwitched was never called

gpu/ipc/service/image_transport_surface_overlay_mac.mm

Index: gpu/ipc/service/image_transport_surface_overlay_mac.mm
diff --git a/gpu/ipc/service/image_transport_surface_overlay_mac.mm b/gpu/ipc/service/image_transport_surface_overlay_mac.mm
index 07e52b65bd80a346e44e9930c73e5a4ef7d2b64c..1c75718e5a7d4830ecc10c27936cd5c7b3b68c49 100644
--- a/gpu/ipc/service/image_transport_surface_overlay_mac.mm
+++ b/gpu/ipc/service/image_transport_surface_overlay_mac.mm
@@ -190,7 +190,7 @@ void IOSurfaceContextNoOp(scoped_refptr<ui::IOSurfaceContext>) {
     // If we have gotten more than one frame ahead of GL, wait for the previous
     // frame to complete.
     if (previous_frame_fence_) {
-      TRACE_EVENT0("gpu", "ImageTransportSurfaceOverlayMac::ClientWait");
+      TRACE_EVENT0("gpu", "ClientWait");
 
       // Ensure we are using the context with which the fence was created.
       gl::ScopedCGLSetCurrentContext scoped_set_current(fence_context_obj_);
@@ -222,8 +222,11 @@ void IOSurfaceContextNoOp(scoped_refptr<ui::IOSurfaceContext>) {
                              base::scoped_policy::RETAIN);
 
     // A glFlush is necessary to ensure correct content appears.
-    glFlush();
-    CheckGLErrors("After fence/flush");
+    {
+      TRACE_EVENT0("gpu", "glFlush");
+      glFlush();
+      CheckGLErrors("After fence/flush");
+    }
 
     after_flush_before_commit_time = base::TimeTicks::Now();
     UMA_HISTOGRAM_TIMES("GPU.IOSurface.GLFlushTime",
@@ -231,7 +234,7 @@ void IOSurfaceContextNoOp(scoped_refptr<ui::IOSurfaceContext>) {
   } else {
     // GLFence isn't supported - issue a glFinish on each frame to ensure
     // there is backpressure from GL.
-    TRACE_EVENT0("gpu", "ImageTransportSurfaceOverlayMac::glFinish");
+    TRACE_EVENT0("gpu", "glFinish");
     CheckGLErrors("Before finish");
     glFinish();
     CheckGLErrors("After finish");
@@ -239,8 +242,11 @@ void IOSurfaceContextNoOp(scoped_refptr<ui::IOSurfaceContext>) {
   }
 
   bool fullscreen_low_power_layer_valid = false;
-  ca_layer_tree_coordinator_->CommitPendingTreesToCA(
-      pixel_damage_rect, &fullscreen_low_power_layer_valid);
+  {
+    TRACE_EVENT0("gpu", "CommitPendingTreesToCA");
+    ca_layer_tree_coordinator_->CommitPendingTreesToCA(
+        pixel_damage_rect, &fullscreen_low_power_layer_valid);
+  }
 
   base::TimeTicks after_transaction_time = base::TimeTicks::Now();
   UMA_HISTOGRAM_TIMES("GPU.IOSurface.CATransactionTime",