Add gpu::BufferBacking::shared_memory_handle()

This CL adds a base::SharedMemoryHandle getter to gpu::BufferBacking.
The getter will be used by gpu::BufferBacking users when OnMemoryDump is
called to create base::SharedMemory dumps.

This is part of work for exposing SharedMemory usages on tracing
memory-infra dumps.

Design doc: https://docs.google.com/document/d/16Mi5_puxKgQ-9IX7ANfbji0WiqBCK3yrnJ0Qi2wa3w0/edit#heading=h.lofdeze1a2hr

Note: This can conflict with https://codereview.chromium.org/2912723002/

BUG=604726
TEST=gpu_unittests --gtest_filter=Buffer.*
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.android:android_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel

Review-Url: https://codereview.chromium.org/2909003002
Cr-Commit-Position: refs/heads/master@{#475837}

gpu/BUILD.gn

@@ -232,6 +232,7 @@ test("gpu_unittests") {
     "command_buffer/client/vertex_array_object_manager_unittest.cc",
     "command_buffer/common/activity_flags_unittest.cc",
     "command_buffer/common/bitfield_helpers_test.cc",
+    "command_buffer/common/buffer_unittest.cc",
     "command_buffer/common/command_buffer_shared_test.cc",
     "command_buffer/common/debug_marker_manager_unittest.cc",
     "command_buffer/common/discardable_handle_unittest.cc",

gpu/command_buffer/common/buffer.cc

@@ -18,6 +18,10 @@ bool BufferBacking::is_shared() const {
   return false;
 }
 
+base::SharedMemoryHandle BufferBacking::shared_memory_handle() const {
+  return base::SharedMemoryHandle();
+}
+
 SharedMemoryBufferBacking::SharedMemoryBufferBacking(
     std::unique_ptr<base::SharedMemory> shared_memory,
     size_t size)
@@ -29,6 +33,11 @@ bool SharedMemoryBufferBacking::is_shared() const {
   return true;
 }
 
+base::SharedMemoryHandle SharedMemoryBufferBacking::shared_memory_handle()
+    const {
+  return shared_memory_->handle();
+}
+
 void* SharedMemoryBufferBacking::GetMemory() const {
   return shared_memory_->memory();
 }

gpu/command_buffer/common/buffer.h

@@ -17,8 +17,11 @@
 #include "gpu/gpu_export.h"
 
 namespace base {
-  class SharedMemory;
-}
+
+class SharedMemory;
+class SharedMemoryHandle;
+
+}  // namespace base
 
 namespace gpu {
 
@@ -26,6 +29,7 @@ class GPU_EXPORT BufferBacking {
  public:
   virtual ~BufferBacking() {}
   virtual bool is_shared() const;
+  virtual base::SharedMemoryHandle shared_memory_handle() const;
   virtual void* GetMemory() const = 0;
   virtual size_t GetSize() const = 0;
 };
@@ -36,6 +40,7 @@ class GPU_EXPORT SharedMemoryBufferBacking : public BufferBacking {
                             size_t size);
   ~SharedMemoryBufferBacking() override;
   bool is_shared() const override;
+  base::SharedMemoryHandle shared_memory_handle() const override;
   void* GetMemory() const override;
   size_t GetSize() const override;
   base::SharedMemory* shared_memory() { return shared_memory_.get(); }

gpu/command_buffer/common/buffer_unittest.cc

+// Copyright 2017 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 "gpu/command_buffer/common/buffer.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace gpu {
+
+TEST(Buffer, SharedMemoryHandle) {
+  const size_t kSize = 1024;
+  std::unique_ptr<base::SharedMemory> shared_memory(new base::SharedMemory);
+  shared_memory->CreateAndMapAnonymous(kSize);
+  auto shared_memory_guid = shared_memory->handle().GetGUID();
+  scoped_refptr<Buffer> buffer =
+      MakeBufferFromSharedMemory(std::move(shared_memory), kSize);
+  EXPECT_EQ(buffer->backing()->shared_memory_handle().GetGUID(),
+            shared_memory_guid);
+}
+
+}  // namespace gpu