Do not consume Alt-Shift-Up event for IME switch.

ash/ime_control_delegate.h

Index: ash/ime_control_delegate.h
diff --git a/ash/ime_control_delegate.h b/ash/ime_control_delegate.h
index 6aa560902d809415065d8ee112f213484240999d..92bef4e092180dea0bc251fef302c96b43e513c5 100644
--- a/ash/ime_control_delegate.h
+++ b/ash/ime_control_delegate.h
@@ -16,8 +16,15 @@ class ImeControlDelegate {
  public:
   virtual ~ImeControlDelegate() {}
 
-  virtual bool HandleNextIme() = 0;
+  // Changes the IME to what is listed next. This function do nothing if there
+  // is only one IME is enabled.
+  virtual void HandleNextIme() = 0;
+
+  // Changes the IME to previously selected one. If there is no previously
+  // selected IMEs, chooses the next listed IME. This function returns false if
+  // there is only one IME is enabled.
   virtual bool HandlePreviousIme(const ui::Accelerator& accelerator) = 0;
+
   // Switches to another IME depending on the |accelerator|.
   virtual bool HandleSwitchIme(const ui::Accelerator& accelerator) = 0;