Refactor gpu::Buffer to allow different types of backing

gpu/command_buffer/service/command_buffer_service.cc

Index: gpu/command_buffer/service/command_buffer_service.cc
diff --git a/gpu/command_buffer/service/command_buffer_service.cc b/gpu/command_buffer/service/command_buffer_service.cc
index df2bd074273b45c6685bdc15b861bc77d5c462ae..30617c8ffa53754fea204e00d485ec1d2aca3fc5 100644
--- a/gpu/command_buffer/service/command_buffer_service.cc
+++ b/gpu/command_buffer/service/command_buffer_service.cc
@@ -103,17 +103,15 @@ void CommandBufferService::SetGetBuffer(int32 transfer_buffer_id) {
   UpdateState();
 }
 
-bool CommandBufferService::SetSharedStateBuffer(
-    scoped_ptr<base::SharedMemory> shared_state_shm) {
-  shared_state_shm_.reset(shared_state_shm.release());
-  if (!shared_state_shm_->Map(sizeof(*shared_state_)))
-    return false;
+void CommandBufferService::SetSharedStateBuffer(
+    scoped_ptr<BufferBacking> shared_state_buffer) {
+  shared_state_buffer_ = shared_state_buffer.Pass();
+  DCHECK(shared_state_buffer_->GetSize() >= sizeof(*shared_state_));
 
   shared_state_ =
-      static_cast<CommandBufferSharedState*>(shared_state_shm_->memory());
+      static_cast<CommandBufferSharedState*>(shared_state_buffer_->GetMemory());
 
   UpdateState();
-  return true;
 }
 
 void CommandBufferService::SetGetOffset(int32 get_offset) {
@@ -132,7 +130,8 @@ scoped_refptr<Buffer> CommandBufferService::CreateTransferBuffer(size_t size,
   static int32 next_id = 1;
   *id = next_id++;
 
-  if (!RegisterTransferBuffer(*id, shared_memory.Pass(), size)) {
+  if (!RegisterTransferBuffer(
+          *id, MakeBackingFromSharedMemory(shared_memory.Pass(), size))) {
     *id = -1;
     return NULL;
   }
@@ -157,10 +156,8 @@ scoped_refptr<Buffer> CommandBufferService::GetTransferBuffer(int32 id) {
 
 bool CommandBufferService::RegisterTransferBuffer(
     int32 id,
-    scoped_ptr<base::SharedMemory> shared_memory,
-    size_t size) {
-  return transfer_buffer_manager_->RegisterTransferBuffer(
-      id, shared_memory.Pass(), size);
+    scoped_ptr<BufferBacking> buffer) {
+  return transfer_buffer_manager_->RegisterTransferBuffer(id, buffer.Pass());
 }
 
 void CommandBufferService::SetToken(int32 token) {