gpu: Directly cast ClientBuffer to gfx::GpuMemoryBuffer

cc/test/test_gpu_memory_buffer_manager.cc

Index: cc/test/test_gpu_memory_buffer_manager.cc
diff --git a/cc/test/test_gpu_memory_buffer_manager.cc b/cc/test/test_gpu_memory_buffer_manager.cc
index fdf073e56ff4da02a855312541f28c1472a2e976..12aa1ee119e873d0633a1facda6a30ffa819ab7b 100644
--- a/cc/test/test_gpu_memory_buffer_manager.cc
+++ b/cc/test/test_gpu_memory_buffer_manager.cc
@@ -189,12 +189,6 @@ TestGpuMemoryBufferManager::CreateGpuMemoryBufferFromHandle(
   return result;
 }
 
-gfx::GpuMemoryBuffer*
-TestGpuMemoryBufferManager::GpuMemoryBufferFromClientBuffer(
-    ClientBuffer buffer) {
-  return reinterpret_cast<gfx::GpuMemoryBuffer*>(buffer);
-}
-
 void TestGpuMemoryBufferManager::SetDestructionSyncToken(
     gfx::GpuMemoryBuffer* buffer,
     const gpu::SyncToken& sync_token) {}