Handle UNPIN operation in ash.

ash/accelerators/accelerator_commands.h

Index: ash/accelerators/accelerator_commands.h
diff --git a/ash/accelerators/accelerator_commands.h b/ash/accelerators/accelerator_commands.h
index e35ab2a5a62c1e32ebc27ef3ec2e5182fa0d131f..832dda39a0891ec6cdc303987a222c38362cfa77 100644
--- a/ash/accelerators/accelerator_commands.h
+++ b/ash/accelerators/accelerator_commands.h
@@ -37,6 +37,9 @@ ASH_EXPORT bool ZoomInternalDisplay(bool up);
 // Reset the display zooming to the default state.
 ASH_EXPORT void ResetInternalDisplayZoom();
 
+// If it is in the pinned mode, exit from it.
+ASH_EXPORT void Unpin();
+
 }  // namespace accelerators
 }  // namespace ash