Remove LayerTreeFrameSink |must_always_swap|.

Forcing LayerTreeHostImpl to always swap shouldn't be necessary for the
browser UI compositor anymore. LayerTreeHostImpl has been changed to
always submit a CompositorFrame if the set of referenced surfaces has
changed.

It appears |must_always_swap| isn't necessary for layout tests either as
they still pass without it.

Bug: 851616
Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: I032264a23ba3b8c880f10d777cbe7b24372f0347
Reviewed-on: https://chromium-review.googlesource.com/1136804Reviewed-by: vmpstr <vmpstr@chromium.org>
Commit-Queue: kylechar <kylechar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#575777}

cc/trees/layer_tree_frame_sink.h

@@ -44,17 +44,6 @@ class LayerTreeFrameSinkClient;
 class CC_EXPORT LayerTreeFrameSink : public viz::SharedBitmapReporter,
                                      public viz::ContextLostObserver {
  public:
-  struct Capabilities {
-    Capabilities() = default;
-
-    // True if we must always swap, even if there is no damage to the frame.
-    // Needed for both the browser compositor as well as layout tests.
-    // TODO(ericrk): This should be test-only for layout tests, but tab
-    // capture has issues capturing offscreen tabs whithout this. We should
-    // remove this dependency. crbug.com/680196
-    bool must_always_swap = false;
-  };
-
   // Constructor for GL-based and/or software resources.
   //
   // |compositor_task_runner| is used to post worker context lost callback and
@@ -92,8 +81,6 @@ class CC_EXPORT LayerTreeFrameSink : public viz::SharedBitmapReporter,
 
   bool HasClient() { return !!client_; }
 
-  const Capabilities& capabilities() const { return capabilities_; }
-
   // The viz::ContextProviders may be null if frames should be submitted with
   // software SharedMemory resources.
   viz::ContextProvider* context_provider() const {
@@ -138,7 +125,6 @@ class CC_EXPORT LayerTreeFrameSink : public viz::SharedBitmapReporter,
 
   LayerTreeFrameSinkClient* client_ = nullptr;
 
-  struct LayerTreeFrameSink::Capabilities capabilities_;
   scoped_refptr<viz::ContextProvider> context_provider_;
   scoped_refptr<viz::RasterContextProvider> worker_context_provider_;
   scoped_refptr<base::SingleThreadTaskRunner> compositor_task_runner_;

cc/trees/layer_tree_host_impl.cc

@@ -968,12 +968,10 @@ bool LayerTreeHostImpl::HasDamage() const {
       root_surface->GetDamageRect().Intersects(root_surface->content_rect());
   bool hud_wants_to_draw_ = active_tree->hud_layer() &&
                             active_tree->hud_layer()->IsAnimatingHUDContents();
-  bool must_always_swap =
-      layer_tree_frame_sink_->capabilities().must_always_swap;
 
   return root_surface_has_visible_damage ||
          active_tree_->property_trees()->effect_tree.HasCopyRequests() ||
-         must_always_swap || hud_wants_to_draw_;
+         hud_wants_to_draw_;
 }
 
 DrawResult LayerTreeHostImpl::CalculateRenderPasses(FrameData* frame) {

components/viz/service/frame_sinks/direct_layer_tree_frame_sink.cc

@@ -46,7 +46,6 @@ DirectLayerTreeFrameSink::DirectLayerTreeFrameSink(
       use_viz_hit_test_(use_viz_hit_test),
       weak_factory_(this) {
   DCHECK_CALLED_ON_VALID_THREAD(thread_checker_);
-  capabilities_.must_always_swap = true;
 }
 
 DirectLayerTreeFrameSink::~DirectLayerTreeFrameSink() {