cc: Add null checks for GrContext created by ContextProviderCommandBuffer.

cc/trees/layer_tree_host_impl.cc

 // Copyright 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/trees/layer_tree_host_impl.h"
 
 #include <algorithm>
 #include <limits>
 #include <map>
 #include <set>
@@ skipping 1566 matching lines @@
   // Once all layers have been drawn, pending texture uploads should no
   // longer block future uploads.
   resource_provider_->MarkPendingUploadsAsNonBlocking();
 }
 
 void LayerTreeHostImpl::FinishAllRendering() {
   if (renderer_)
     renderer_->Finish();
 }
 
+bool LayerTreeHostImpl::CanUseGpuRasterization() {
+  if (!(output_surface_ && output_surface_->context_provider() &&
+        output_surface_->worker_context_provider()))
+    return false;
+
+  ContextProvider* context_provider =
+      output_surface_->worker_context_provider();
+  base::AutoLock context_lock(*context_provider->GetLock());
+  if (!context_provider->GrContext())
+    return false;
+
+  return true;
+}
+
 void LayerTreeHostImpl::UpdateGpuRasterizationStatus() {
   bool use_gpu = false;
   bool use_msaa = false;
   bool using_msaa_for_complex_content =
       renderer() && settings_.gpu_rasterization_msaa_sample_count > 0 &&
       GetRendererCapabilities().max_msaa_samples >=
           settings_.gpu_rasterization_msaa_sample_count;
   if (settings_.gpu_rasterization_forced) {
     use_gpu = true;
     gpu_rasterization_status_ = GpuRasterizationStatus::ON_FORCED;
     use_msaa = !content_is_suitable_for_gpu_rasterization_ &&
                using_msaa_for_complex_content;
     if (use_msaa) {
       gpu_rasterization_status_ = GpuRasterizationStatus::MSAA_CONTENT;
     }
   } else if (!settings_.gpu_rasterization_enabled) {
     gpu_rasterization_status_ = GpuRasterizationStatus::OFF_DEVICE;
   } else if (!has_gpu_rasterization_trigger_) {
     gpu_rasterization_status_ = GpuRasterizationStatus::OFF_VIEWPORT;
   } else if (content_is_suitable_for_gpu_rasterization_) {
     use_gpu = true;
     gpu_rasterization_status_ = GpuRasterizationStatus::ON;
   } else if (using_msaa_for_complex_content) {
     use_gpu = use_msaa = true;
     gpu_rasterization_status_ = GpuRasterizationStatus::MSAA_CONTENT;
   } else {
     gpu_rasterization_status_ = GpuRasterizationStatus::OFF_CONTENT;
   }
 
+  if (use_gpu && !use_gpu_rasterization_) {
+    if (!CanUseGpuRasterization()) {
+      // If GPU rasterization is unusable, e.g. if GlContext could not
+      // be created due to losing the GL context, force use of software
+      // raster.
+      use_gpu = false;
+      use_msaa = false;
+      gpu_rasterization_status_ = GpuRasterizationStatus::OFF_DEVICE;
+    }
+  }
+
   if (use_gpu == use_gpu_rasterization_ && use_msaa == use_msaa_)
     return;
 
   // Note that this must happen first, in case the rest of the calls want to
   // query the new state of |use_gpu_rasterization_|.
   use_gpu_rasterization_ = use_gpu;
   use_msaa_ = use_msaa;
 
   // Clean up and replace existing tile manager with another one that uses
   // appropriate rasterizer.
@@ skipping 1770 matching lines @@
   new_target.SetToMin(layer_impl->MaxScrollOffset());
 
   curve->UpdateTarget(
       animation->TrimTimeToCurrentIteration(CurrentBeginFrameArgs().frame_time)
           .InSecondsF(),
       new_target);
 
   return true;
 }
 }  // namespace cc