Add a command-line flag to enable threaded GPU rasterization.

For now a no-op in the renderer.

Enable:
  --enable-threaded-gpu-rasterization

Disable (which takes priority over Enable):
  --disable-threaded-gpu-rasterization

BUG=454500

Review URL: https://codereview.chromium.org/895763002

Cr-Commit-Position: refs/heads/master@{#314418}

6 files changed, 17 insertions, 15 deletions

diff --git a/cc/resources/gpu_rasterizer.cc b/cc/resources/gpu_rasterizer.cc
index 3fdc8bb..369f12c 100644
--- a/cc/resources/gpu_rasterizer.cc
+++ b/cc/resources/gpu_rasterizer.cc
@@ -31,22 +31,22 @@ scoped_ptr<GpuRasterizer> GpuRasterizer::Create(
     ContextProvider* context_provider,
     ResourceProvider* resource_provider,
     bool use_distance_field_text,
-    bool tile_prepare_enabled,
+    bool threaded_gpu_rasterization_enabled,
     int msaa_sample_count) {
   return make_scoped_ptr<GpuRasterizer>(new GpuRasterizer(
       context_provider, resource_provider, use_distance_field_text,
-      tile_prepare_enabled, msaa_sample_count));
+      threaded_gpu_rasterization_enabled, msaa_sample_count));
 }
 
 GpuRasterizer::GpuRasterizer(ContextProvider* context_provider,
                              ResourceProvider* resource_provider,
                              bool use_distance_field_text,
-                             bool tile_prepare_enabled,
+                             bool threaded_gpu_rasterization_enabled,
                              int msaa_sample_count)
     : context_provider_(context_provider),
       resource_provider_(resource_provider),
       use_distance_field_text_(use_distance_field_text),
-      tile_prepare_enabled_(tile_prepare_enabled),
+      threaded_gpu_rasterization_enabled_(threaded_gpu_rasterization_enabled),
       msaa_sample_count_(msaa_sample_count) {
   DCHECK(context_provider_);
 }
@@ -55,8 +55,7 @@ GpuRasterizer::~GpuRasterizer() {
 }
 
 PrepareTilesMode GpuRasterizer::GetPrepareTilesMode() {
-  return tile_prepare_enabled_ ? PrepareTilesMode::PREPARE_PRIORITIZED_TILES
-                               : PrepareTilesMode::PREPARE_NONE;
+  return PrepareTilesMode::PREPARE_NONE;
 }
 
 void GpuRasterizer::RasterizeTiles(
diff --git a/cc/resources/gpu_rasterizer.h b/cc/resources/gpu_rasterizer.h
index 206b051..79a0596 100644
--- a/cc/resources/gpu_rasterizer.h
+++ b/cc/resources/gpu_rasterizer.h
@@ -22,11 +22,12 @@ class CC_EXPORT GpuRasterizer : public Rasterizer {
  public:
   ~GpuRasterizer() override;
 
-  static scoped_ptr<GpuRasterizer> Create(ContextProvider* context_provider,
-                                          ResourceProvider* resource_provider,
-                                          bool use_distance_field_text,
-                                          bool tile_prepare_enabled,
-                                          int msaa_sample_count);
+  static scoped_ptr<GpuRasterizer> Create(
+      ContextProvider* context_provider,
+      ResourceProvider* resource_provider,
+      bool use_distance_field_text,
+      bool threaded_gpu_rasterization_enabled,
+      int msaa_sample_count);
   PrepareTilesMode GetPrepareTilesMode() override;
   void RasterizeTiles(
       const TileVector& tiles,
@@ -38,7 +39,7 @@ class CC_EXPORT GpuRasterizer : public Rasterizer {
   GpuRasterizer(ContextProvider* context_provider,
                 ResourceProvider* resource_provider,
                 bool use_distance_filed_text,
-                bool tile_prepare_enabled,
+                bool threaded_gpu_rasterization_enabled,
                 int msaa_sample_count);
 
   using ScopedResourceWriteLocks =
@@ -55,7 +56,7 @@ class CC_EXPORT GpuRasterizer : public Rasterizer {
   SkMultiPictureDraw multi_picture_draw_;
 
   bool use_distance_field_text_;
-  bool tile_prepare_enabled_;
+  bool threaded_gpu_rasterization_enabled_;
   int msaa_sample_count_;
 
   DISALLOW_COPY_AND_ASSIGN(GpuRasterizer);
diff --git a/cc/resources/rasterizer.h b/cc/resources/rasterizer.h
index 95b9ce2..43df0b0 100644
--- a/cc/resources/rasterizer.h
+++ b/cc/resources/rasterizer.h
@@ -16,7 +16,6 @@ class TileManager;
 
 enum class PrepareTilesMode {
   RASTERIZE_PRIORITIZED_TILES,
-  PREPARE_PRIORITIZED_TILES,
   PREPARE_NONE
 };
 
diff --git a/cc/trees/layer_tree_host_impl.cc b/cc/trees/layer_tree_host_impl.cc
index c8ee69c..34278c6 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -1977,7 +1977,8 @@ scoped_ptr<Rasterizer> LayerTreeHostImpl::CreateRasterizer() {
   ContextProvider* context_provider = output_surface_->context_provider();
   if (use_gpu_rasterization_ && context_provider) {
     return GpuRasterizer::Create(context_provider, resource_provider_.get(),
-                                 settings_.use_distance_field_text, false,
+                                 settings_.use_distance_field_text,
+                                 settings_.threaded_gpu_rasterization_enabled,
                                  settings_.gpu_rasterization_msaa_sample_count);
   }
   return SoftwareRasterizer::Create();
diff --git a/cc/trees/layer_tree_settings.cc b/cc/trees/layer_tree_settings.cc
index d578daf..07dfc29 100644
--- a/cc/trees/layer_tree_settings.cc
+++ b/cc/trees/layer_tree_settings.cc
@@ -30,6 +30,7 @@ LayerTreeSettings::LayerTreeSettings()
       gpu_rasterization_enabled(false),
       gpu_rasterization_forced(false),
       gpu_rasterization_msaa_sample_count(0),
+      threaded_gpu_rasterization_enabled(false),
       create_low_res_tiling(false),
       scrollbar_animator(NoAnimator),
       scrollbar_fade_delay_ms(0),
diff --git a/cc/trees/layer_tree_settings.h b/cc/trees/layer_tree_settings.h
index 597a279..5eacdf8 100644
--- a/cc/trees/layer_tree_settings.h
+++ b/cc/trees/layer_tree_settings.h
@@ -36,6 +36,7 @@ class CC_EXPORT LayerTreeSettings {
   bool gpu_rasterization_enabled;
   bool gpu_rasterization_forced;
   int gpu_rasterization_msaa_sample_count;
+  bool threaded_gpu_rasterization_enabled;
   bool create_low_res_tiling;
 
   enum ScrollbarAnimator {