Replaced is_null() with is_valid in SurfaceId and related classes.

content/browser/frame_host/render_widget_host_view_guest.cc

Index: content/browser/frame_host/render_widget_host_view_guest.cc
diff --git a/content/browser/frame_host/render_widget_host_view_guest.cc b/content/browser/frame_host/render_widget_host_view_guest.cc
index 6454b5866eb60790ee7adb87ceb0b6e27bd13134..3b27c226679cef917f3e6241d2af4c38077b33ef 100644
--- a/content/browser/frame_host/render_widget_host_view_guest.cc
+++ b/content/browser/frame_host/render_widget_host_view_guest.cc
@@ -123,7 +123,7 @@ void RenderWidgetHostViewGuest::Show() {
     // Since we were last shown, our renderer may have had a different surface
     // set (e.g. showing an interstitial), so we resend our current surface to
     // the renderer.
-    if (!local_frame_id_.is_null()) {
+    if (local_frame_id_.is_valid()) {
       cc::SurfaceSequence sequence =
           cc::SurfaceSequence(frame_sink_id_, next_surface_sequence_++);
       cc::SurfaceId surface_id(frame_sink_id_, local_frame_id_);
@@ -308,7 +308,7 @@ void RenderWidgetHostViewGuest::OnSwapCompositorFrame(
         base::MakeUnique<cc::SurfaceFactory>(frame_sink_id_, manager, this);
   }
 
-  if (local_frame_id_.is_null()) {
+  if (!local_frame_id_.is_valid()) {
     local_frame_id_ = id_allocator_->GenerateId();
     surface_factory_->Create(local_frame_id_);