Check that shared memory GpuMemoryBuffer opening succeeds

content/common/gpu/client/gpu_memory_buffer_impl_shared_memory.cc

Index: content/common/gpu/client/gpu_memory_buffer_impl_shared_memory.cc
diff --git a/content/common/gpu/client/gpu_memory_buffer_impl_shared_memory.cc b/content/common/gpu/client/gpu_memory_buffer_impl_shared_memory.cc
index 8b840739d4cdceda70bd77219ce241781ccbcf09..11f54c40d9c659255c9d8b36a9be15976295c662 100644
--- a/content/common/gpu/client/gpu_memory_buffer_impl_shared_memory.cc
+++ b/content/common/gpu/client/gpu_memory_buffer_impl_shared_memory.cc
@@ -87,8 +87,7 @@ GpuMemoryBufferImplSharedMemory::CreateFromHandle(
     gfx::BufferFormat format,
     gfx::BufferUsage usage,
     const DestructionCallback& callback) {
-  if (!base::SharedMemory::IsHandleValid(handle.handle))
-    return nullptr;
+  DCHECK(base::SharedMemory::IsHandleValid(handle.handle));
 
   return make_scoped_ptr(new GpuMemoryBufferImplSharedMemory(
       handle.id, size, format, callback,