Add gfx::GpuMemoryBuffer::shared_memory_handle()

gpu/ipc/client/gpu_memory_buffer_impl_shared_memory_unittest.cc

Index: gpu/ipc/client/gpu_memory_buffer_impl_shared_memory_unittest.cc
diff --git a/gpu/ipc/client/gpu_memory_buffer_impl_shared_memory_unittest.cc b/gpu/ipc/client/gpu_memory_buffer_impl_shared_memory_unittest.cc
index 257b64e750c630120220246e43acc2a0473276e0..5a77a0c69834c20190edb991358189d51e00eb41 100644
--- a/gpu/ipc/client/gpu_memory_buffer_impl_shared_memory_unittest.cc
+++ b/gpu/ipc/client/gpu_memory_buffer_impl_shared_memory_unittest.cc
@@ -32,6 +32,10 @@ TEST(GpuMemoryBufferImplSharedMemoryTest, Create) {
     ASSERT_TRUE(buffer);
     EXPECT_EQ(buffer->GetFormat(), format);
 
+    // Check if the backend is actually SharedMemory and its GUID is available.
+    EXPECT_NE(base::UnguessableToken(),
+              buffer->shared_memory_handle().GetGUID());
+
     // Check if destruction callback is executed when deleting the buffer.
     buffer.reset();
     ASSERT_TRUE(destroyed);