gpu: Refactor GpuMemoryBuffer framework for multi-process support.

cc/resources/pixel_buffer_raster_worker_pool.cc

Index: cc/resources/pixel_buffer_raster_worker_pool.cc
diff --git a/cc/resources/pixel_buffer_raster_worker_pool.cc b/cc/resources/pixel_buffer_raster_worker_pool.cc
index a03ed81f4e1df836f8c44c029421ebc0a819d26b..761880387b1d1120e8123691e7321cb98602d43b 100644
--- a/cc/resources/pixel_buffer_raster_worker_pool.cc
+++ b/cc/resources/pixel_buffer_raster_worker_pool.cc
@@ -236,6 +236,10 @@ void PixelBufferRasterWorkerPool::ScheduleTasks(RasterTask::Queue* queue) {
       "state", TracedValue::FromValue(StateAsValue().release()));
 }
 
+GLenum PixelBufferRasterWorkerPool::GetResourceFormat() const {
+  return resource_provider()->best_texture_format();
+}
+
 void PixelBufferRasterWorkerPool::CheckForCompletedTasks() {
   TRACE_EVENT0("cc", "PixelBufferRasterWorkerPool::CheckForCompletedTasks");