ui: Add out-of-line copy ctors for complex classes.

ui/gfx/gpu_memory_buffer.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/gfx/gpu_memory_buffer.h"
 
 namespace gfx {
 
 base::trace_event::MemoryAllocatorDumpGuid GetGpuMemoryBufferGUIDForTracing(
     uint64_t tracing_process_id,
     GpuMemoryBufferId buffer_id) {
   // TODO(ericrk): Currently this function just wraps
   // GetGenericSharedMemoryGUIDForTracing, we may want to special case this if
   // the GPU memory buffer is not backed by shared memory.
   return gfx::GetGenericSharedMemoryGUIDForTracing(tracing_process_id,
                                                    buffer_id);
 }
 
 GpuMemoryBufferHandle::GpuMemoryBufferHandle()
     : type(EMPTY_BUFFER), id(0), handle(base::SharedMemory::NULLHandle()) {
 }
 
+GpuMemoryBufferHandle::GpuMemoryBufferHandle(
+    const GpuMemoryBufferHandle& other) = default;
+
 GpuMemoryBufferHandle::~GpuMemoryBufferHandle() {}
 
 bool GpuMemoryBuffer::IsInUseByMacOSWindowServer() const {
   return false;
 }
 
 }  // namespace gfx