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 2148 matching lines @@
   resource_provider_ = nullptr;
   output_surface_ = nullptr;
 
   if (!output_surface->BindToClient(this)) {
     // Avoid recreating tree resources because we might not have enough
     // information to do this yet (eg. we don't have a TileManager at this
     // point).
     return false;
   }
 
+  if (use_gpu_rasterization_) {

[danakj, 2015/05/12 23:40:43]

This can be changed by CreateAndSetRenderer below and suddenly become true I
think (I was hoping it was a one-way trip from true to false but the code
doesn't look like that to me.)

But maybe you can make UpdateGpuRasterizationStatus() before this. It's using
renderercaps but only as a proxy for the contextprovider caps. It's also
recreating layer resources and stuff which would maybe need to be split into
another function to run at the time when it currently is.

[vmiura, 2015/05/13 02:53:00]

Thanks for spotting this.

Hmm, I think it could also flip from false to true in
UpdateGpuRasterizationStatus()
via CommitComplete().

This doesn't look good to me anymore; we can handle failure in
InitializeRenderer() but after that I think the code assumes that
UpdateGpuRasterizationStatus() succeeds.

I'm thinking it's safer to back to "ifs" in the several places where GrContext()
is used, with big TODOs to remove them when GrContext can handle failure.

[piman, 2015/05/13 03:28:36]

We can simply rely on settings_.gpu_rasterization_enabled instead. If we /may/
use gpu rasterization, we should check the GrContext. Otherwise, we don't care.

[Stephen White, 2015/05/13 10:10:13]

In that case, you should probably check settings_.gpu_rasterization_forced as
well.

+    // Ensure we have a GrContext for GPU rasterization.
+    ContextProvider* context_provider =
+        output_surface->worker_context_provider();
+    if (!context_provider)

[piman, 2015/05/12 23:33:50]

nit: you can probably DCHECK this.

+      return false;
+    if (!context_provider->GrContext())
+      return false;
+  }
+
   output_surface_ = output_surface.Pass();
   resource_provider_ = ResourceProvider::Create(
       output_surface_.get(), shared_bitmap_manager_, gpu_memory_buffer_manager_,
       proxy_->blocking_main_thread_task_runner(),
       settings_.renderer_settings.highp_threshold_min,
       settings_.renderer_settings.use_rgba_4444_textures,
       settings_.renderer_settings.texture_id_allocation_chunk_size);
 
   CreateAndSetRenderer();
 
@@ skipping 1220 matching lines @@
   new_target.SetToMin(layer_impl->MaxScrollOffset());
 
   curve->UpdateTarget(
       animation->TrimTimeToCurrentIteration(CurrentBeginFrameArgs().frame_time)
           .InSecondsF(),
       new_target);
 
   return true;
 }
 }  // namespace cc