Add GenericSharedMemoryId and use w/ 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 d70b74083c9ddef19ffc3f48653654935191e616..34cb2494e4bb003e44176042bc75b707c56fa260 100644
--- a/cc/test/test_gpu_memory_buffer_manager.cc
+++ b/cc/test/test_gpu_memory_buffer_manager.cc
@@ -133,7 +133,7 @@ class GpuMemoryBufferImpl : public gfx::GpuMemoryBuffer {
   }
   gfx::GpuMemoryBufferId GetId() const override {
     NOTREACHED();
-    return 0;
+    return gfx::GpuMemoryBufferId(0);
   }
   gfx::GpuMemoryBufferHandle GetHandle() const override {
     gfx::GpuMemoryBufferHandle handle;