cc: Add raster_enabled setting

In order to support impl-side painting plus an embedder without a
message loop, cc needs a setting to disable raster.  Rastering with
impl-side painting requires a task runner (and DCHECKs this).  This
setting notifies cc that there's no need for a tile manager.

Thankfully, tile manager is already considered optional in almost all
contexts, and so just a few more callsites needed to be cleaned up to
fix a few crashes.

With this patch, all cc unittests pass with impl-side painting on by
default.

Review URL: https://codereview.chromium.org/984113004

Cr-Commit-Position: refs/heads/master@{#319840}

cc/layers/picture_layer.cc

@@ -79,20 +79,23 @@ void PictureLayer::PushPropertiesTo(LayerImpl* base_layer) {
 
 void PictureLayer::SetLayerTreeHost(LayerTreeHost* host) {
   Layer::SetLayerTreeHost(host);
-  if (host) {
-    if (!recording_source_) {
-      if (host->settings().use_display_lists) {
-        recording_source_.reset(new DisplayListRecordingSource);
-      } else {
-        recording_source_.reset(
-            new PicturePile(host->settings().minimum_contents_scale,
-                            host->settings().default_tile_grid_size));
-      }
+  if (!host)
+    return;
+
+  if (!recording_source_) {
+    if (host->settings().use_display_lists) {
+      recording_source_.reset(new DisplayListRecordingSource);
+    } else {
+      recording_source_.reset(
+          new PicturePile(host->settings().minimum_contents_scale,
+                          host->settings().default_tile_grid_size));
     }
-    recording_source_->DidMoveToNewCompositor();
-    recording_source_->SetSlowdownRasterScaleFactor(
-        host->debug_state().slow_down_raster_scale_factor);
   }
+  recording_source_->DidMoveToNewCompositor();
+  recording_source_->SetSlowdownRasterScaleFactor(
+      host->debug_state().slow_down_raster_scale_factor);
+
+  DCHECK(host->settings().raster_enabled);
 }
 
 void PictureLayer::SetNeedsDisplayRect(const gfx::Rect& layer_rect) {

cc/trees/layer_tree_host_impl.cc

@@ -1055,7 +1055,7 @@ DrawResult LayerTreeHostImpl::PrepareToDraw(FrameData* frame) {
   // This will cause NotifyTileStateChanged() to be called for any visible tiles
   // that completed, which will add damage to the frame for them so they appear
   // as part of the current frame being drawn.
-  if (settings().impl_side_painting)
+  if (tile_manager_)
     tile_manager_->UpdateVisibleTiles(global_tile_state_);
 
   frame->render_surface_layer_list = &active_tree_->RenderSurfaceLayerList();
@@ -1705,7 +1705,8 @@ void LayerTreeHostImpl::UpdateViewportContainerSizes() {
 void LayerTreeHostImpl::SynchronouslyInitializeAllTiles() {
   // Only valid for the single-threaded non-scheduled/synchronous case
   // using the zero copy raster worker pool.
-  single_thread_synchronous_task_graph_runner_->RunUntilIdle();
+  if (tile_manager_)
+    single_thread_synchronous_task_graph_runner_->RunUntilIdle();
 }
 
 void LayerTreeHostImpl::DidLoseOutputSurface() {
@@ -2136,7 +2137,7 @@ bool LayerTreeHostImpl::InitializeRenderer(
 
   CreateAndSetRenderer();
 
-  if (settings_.impl_side_painting)
+  if (settings_.impl_side_painting && settings_.raster_enabled)
     CreateAndSetTileManager();
   RecreateTreeResources();
 

cc/trees/layer_tree_host_impl.h

@@ -610,6 +610,7 @@ class CC_EXPORT LayerTreeHostImpl
 
   // |resource_provider_| and |tile_manager_| can be NULL, e.g. when using tile-
   // free rendering - see OutputSurface::ForcedDrawToSoftwareDevice().
+  // |tile_manager_| can also be NULL when raster_enabled is false.
   scoped_ptr<ResourceProvider> resource_provider_;
   scoped_ptr<TileManager> tile_manager_;
   bool use_gpu_rasterization_;

cc/trees/layer_tree_host_unittest_no_message_loop.cc

@@ -104,6 +104,7 @@ class LayerTreeHostNoMessageLoopTest
     LayerTreeSettings settings;
     settings.single_thread_proxy_scheduler = false;
     settings.verify_property_trees = true;
+    settings.raster_enabled = false;
     layer_tree_host_ = LayerTreeHost::CreateSingleThreaded(
         this, this, nullptr, nullptr, settings, nullptr, nullptr);
     layer_tree_host_->SetViewportSize(size_);

cc/trees/layer_tree_settings.cc

@@ -15,6 +15,7 @@ namespace cc {
 
 LayerTreeSettings::LayerTreeSettings()
     : impl_side_painting(false),
+      raster_enabled(true),
       throttle_frame_production(true),
       single_thread_proxy_scheduler(true),
       use_external_begin_frame_source(false),

cc/trees/layer_tree_settings.h

@@ -21,6 +21,7 @@ class CC_EXPORT LayerTreeSettings {
 
   RendererSettings renderer_settings;
   bool impl_side_painting;
+  bool raster_enabled;
   bool throttle_frame_production;
   bool single_thread_proxy_scheduler;
   bool use_external_begin_frame_source;