Fix CompositorFrameSinkSupport::GetSurfaceSize().

Fix two issues with GetSurfaceSize(). First, the Surface could have been
evicted so check if |current_surface| is null. Second, simplify logic by
getting the size_in_pixels() from Surface::surface_info_ since it will
always be the same for active/fallback frame.

Bug: none
Cq-Include-Trybots: master.tryserver.chromium.android:android_optional_gpu_tests_rel
Change-Id: If38f0673c878ebaadba8ee7038b4f677a522bdbe
Reviewed-on: https://chromium-review.googlesource.com/783253Reviewed-by: Yuri Wiitala <miu@chromium.org>
Commit-Queue: kylechar <kylechar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#518452}

components/viz/service/frame_sinks/compositor_frame_sink_support.cc

@@ -404,10 +404,8 @@ gfx::Size CompositorFrameSinkSupport::GetSurfaceSize() {
   if (current_surface_id_.is_valid()) {
     Surface* current_surface =
         surface_manager_->GetSurfaceForId(current_surface_id_);
-    if (current_surface->HasActiveFrame())
-      return current_surface->GetActiveFrame().size_in_pixels();
-    else if (current_surface->HasPendingFrame())
-      return current_surface->GetPendingFrame().size_in_pixels();
+    if (current_surface)
+      return current_surface->size_in_pixels();
   }
   return gfx::Size();
 }

components/viz/service/surfaces/surface.h

@@ -93,6 +93,9 @@ class VIZ_SERVICE_EXPORT Surface final : public SurfaceDeadlineClient {
   const SurfaceId& previous_frame_surface_id() const {
     return previous_frame_surface_id_;
   }
+  const gfx::Size& size_in_pixels() const {
+    return surface_info_.size_in_pixels();
+  }
 
   base::WeakPtr<SurfaceClient> client() { return surface_client_; }