Add MetalayerMode to the palette.

ash/shell/shell_delegate_impl.cc

Index: ash/shell/shell_delegate_impl.cc
diff --git a/ash/shell/shell_delegate_impl.cc b/ash/shell/shell_delegate_impl.cc
index 0baaab39c65d3d941cb4a1da978ffe5e2a6f44d5..7db49147b9cf8a98cb857ad570d46751cc1d6eb8 100644
--- a/ash/shell/shell_delegate_impl.cc
+++ b/ash/shell/shell_delegate_impl.cc
@@ -52,6 +52,9 @@ class PaletteDelegateImpl : public PaletteDelegate {
       done.Run();
   }
   void CancelPartialScreenshot() override {}
+  bool IsMetalayerSupported() override { return false; }
+  void ShowMetalayer(const base::Closure& closed) override {}
+  void HideMetalayer() override {}
 
  private:
   DISALLOW_COPY_AND_ASSIGN(PaletteDelegateImpl);