Add GenericSharedMemoryId and use w/ GpuMemoryBuffer

gpu/command_buffer/tests/gl_manager.cc

Index: gpu/command_buffer/tests/gl_manager.cc
diff --git a/gpu/command_buffer/tests/gl_manager.cc b/gpu/command_buffer/tests/gl_manager.cc
index 7897d1635cd0c3b9e48ad539bd524088d46d20c6..f32792fb49058fb7cb3254a861008e6dc09372fb 100644
--- a/gpu/command_buffer/tests/gl_manager.cc
+++ b/gpu/command_buffer/tests/gl_manager.cc
@@ -145,7 +145,7 @@ class GpuMemoryBufferImpl : public gfx::GpuMemoryBuffer {
   }
   gfx::GpuMemoryBufferId GetId() const override {
     NOTREACHED();
-    return 0;
+    return gfx::GpuMemoryBufferId(0);
   }
   gfx::GpuMemoryBufferHandle GetHandle() const override {
     NOTREACHED();