FrameGenerator to use alloctor's copy

The LSI allocators previously did not store a copy of the last generated
LSI. As a result, many call sites would have to keep their own copies.

Now that the LSI allocators have their own copies, the call sites can be
updated to no longer store a separate copy.

FrameGenerator is one such call site.

BUG=759031

Change-Id: I39774ba04f4bbfd61909e9df12df76c1fd76c492
Reviewed-on: https://chromium-review.googlesource.com/1029427
Commit-Queue: Fady Samuel <fsamuel@chromium.org>
Reviewed-by: Fady Samuel <fsamuel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#553905}

services/ui/ws/frame_generator.cc

@@ -110,16 +110,17 @@ void FrameGenerator::OnBeginFrame(const viz::BeginFrameArgs& begin_frame_args) {
 
   // TODO(fsamuel): We should add a trace for generating a top level frame.
   viz::CompositorFrame frame(GenerateCompositorFrame());
-  if (!local_surface_id_.is_valid() ||
+  if (!id_allocator_.GetCurrentLocalSurfaceId().is_valid() ||
       frame.size_in_pixels() != last_submitted_frame_size_ ||
       frame.device_scale_factor() != last_device_scale_factor_) {
     last_device_scale_factor_ = frame.device_scale_factor();
     last_submitted_frame_size_ = frame.size_in_pixels();
-    local_surface_id_ = id_allocator_.GenerateId();
+    id_allocator_.GenerateId();
   }
 
   compositor_frame_sink_->SubmitCompositorFrame(
-      local_surface_id_, std::move(frame), GenerateHitTestRegionList(), 0);
+      id_allocator_.GetCurrentLocalSurfaceId(), std::move(frame),
+      GenerateHitTestRegionList(), 0);
 
   SetNeedsBeginFrame(false);
 }

services/ui/ws/frame_generator.h

@@ -82,7 +82,6 @@ class FrameGenerator : public viz::mojom::CompositorFrameSinkClient {
   viz::BeginFrameAck current_begin_frame_ack_;
   bool high_contrast_mode_enabled_ = false;
   gfx::Size last_submitted_frame_size_;
-  viz::LocalSurfaceId local_surface_id_;
   viz::ParentLocalSurfaceIdAllocator id_allocator_;
   float last_device_scale_factor_ = 0.0f;