Use mojo volume interfaces for mash and classic ash.

ash/common/accelerators/accelerator_controller.h

Index: ash/common/accelerators/accelerator_controller.h
diff --git a/ash/common/accelerators/accelerator_controller.h b/ash/common/accelerators/accelerator_controller.h
index 6c9741f1ad32d01b7e930c7ec6f89ab78c8e7e32..b48360f17446c6e7bbdbe7d141f7fc6ad96dc48d 100644
--- a/ash/common/accelerators/accelerator_controller.h
+++ b/ash/common/accelerators/accelerator_controller.h
@@ -14,6 +14,7 @@
 #include "ash/ash_export.h"
 #include "ash/common/accelerators/accelerator_table.h"
 #include "ash/common/accelerators/exit_warning_handler.h"
+#include "ash/public/interfaces/volume.mojom.h"
 #include "base/compiler_specific.h"
 #include "base/gtest_prod_util.h"
 #include "base/macros.h"
@@ -155,6 +156,10 @@ class ASH_EXPORT AcceleratorController : public ui::AcceleratorTarget {
   AcceleratorProcessingRestriction GetAcceleratorProcessingRestriction(
       int action);
 
+  // Returns the volume controller interface raw pointer, may be null in tests.
+  mojom::VolumeController* GetVolumeController();
+  void OnVolumeControllerConnectionError();
+
   AcceleratorControllerDelegate* delegate_;
 
   std::unique_ptr<ui::AcceleratorManager> accelerator_manager_;
@@ -176,6 +181,9 @@ class ASH_EXPORT AcceleratorController : public ui::AcceleratorTarget {
       actions_with_deprecations_;
   std::set<ui::Accelerator> deprecated_accelerators_;
 
+  // The cached volume controller interface pointer, implemented in Chrome.

[James Cook, 2016/10/18 23:53:39]

super nit: I might leave off the "implemented in Chrome" bit. The interface
itself describes who implements it, and I was a bit confused at first (I thought
it pointed to an object whose implementation was in chrome :-)

[msw, 2016/10/19 15:24:10]

Done.

+  mojom::VolumeControllerPtr volume_controller_;
+
   // Actions allowed when the user is not signed in.
   std::set<int> actions_allowed_at_login_screen_;
   // Actions allowed when the screen is locked.