cc, gpu: Use RGBA when using msaa on systems that don't support BGRA

cc/raster/gpu_tile_task_worker_pool.cc

Index: cc/raster/gpu_tile_task_worker_pool.cc
diff --git a/cc/raster/gpu_tile_task_worker_pool.cc b/cc/raster/gpu_tile_task_worker_pool.cc
index 3de7118a05d16889b3d295a3f3b1f1af6c03a9d1..e2891e1b5a881b0d42b6eb7e33e7966b4396b029 100644
--- a/cc/raster/gpu_tile_task_worker_pool.cc
+++ b/cc/raster/gpu_tile_task_worker_pool.cc
@@ -208,7 +208,17 @@ void GpuTileTaskWorkerPool::CheckForCompletedTasks() {
 }
 
 ResourceFormat GpuTileTaskWorkerPool::GetResourceFormat() {
-  return rasterizer_->resource_provider()->best_texture_format();
+  ResourceFormat format =

[vmiura, 2015/06/09 23:05:11]

We call this per-tile.  I think it'd be good to pre-calc this and return via
something like ResourceProvider::best_renderbuffer_format().

+      rasterizer_->resource_provider()->best_texture_format();
+  if (rasterizer_->msaa_sample_count()) {
+    const ContextProvider::Capabilities& caps = rasterizer_->resource_provider()
+                                                    ->output_surface()
+                                                    ->context_provider()
+                                                    ->ContextCapabilities();
+    if (!caps.gpu.render_buffer_format_bgra8888)
+      return ResourceFormat::RGBA_8888;
+  }
+  return format;
 }
 
 void GpuTileTaskWorkerPool::CompleteTasks(const Task::Vector& tasks) {