Add MetalayerMode to the palette.

ash/palette_delegate.h

Index: ash/palette_delegate.h
diff --git a/ash/palette_delegate.h b/ash/palette_delegate.h
index 942f09e7cc541a535702374c07a60e68506e86c4..5edf6965647c2e04175b5bf566a7d79e6b5e0646 100644
--- a/ash/palette_delegate.h
+++ b/ash/palette_delegate.h
@@ -54,6 +54,15 @@ class PaletteDelegate {
   // Cancels any active partial screenshot session.
   virtual void CancelPartialScreenshot() = 0;
 
+  // Returns true if the metalayer is available.
+  virtual bool HasMetalayer() = 0;
+
+  // Shows the metalayer.
+  virtual void ShowMetalayer(const base::Closure& done) = 0;

[Luis Héctor Chávez, 2017/04/20 16:03:26]

maybe s/done/closed/ or s/done/interaction_done/ in all ShowMetalayer()
decls/impls?

also, please mention that |closed| is invoked if the metalayer could not be
shown, or when the interaction with the metalayer is done / the metalayer is
closed.

[Vladislav Kaznacheev, 2017/04/20 17:54:55]

going with interaction_done. Added a comment.

+
+  // Hides the metalayer.
+  virtual void HideMetalayer() = 0;
+
  private:
   DISALLOW_ASSIGN(PaletteDelegate);
 };