Moves WorkspaceEventHandler to ash/common

ash/common/wm_shell.h

Index: ash/common/wm_shell.h
diff --git a/ash/common/wm_shell.h b/ash/common/wm_shell.h
index 3db0a06101b8f4178ba92b0bbf246f701d6bb07e..6ec6ba247324872e57f0b2fce21bba0f46ea1723 100644
--- a/ash/common/wm_shell.h
+++ b/ash/common/wm_shell.h
@@ -64,6 +64,7 @@ class WindowSelectorController;
 class WmActivationObserver;
 class WmDisplayObserver;
 class WmWindow;
+class WorkspaceEventHandler;
 
 enum class TaskSwitchSource;
 
@@ -270,6 +271,10 @@ class ASH_EXPORT WmShell {
   virtual std::unique_ptr<wm::MaximizeModeEventHandler>
   CreateMaximizeModeEventHandler() = 0;
 
+  // This may return null.

[James Cook, 2016/08/26 19:07:16]

In tests? In this CL it's non-null for both aura and mus.

[sky, 2016/08/26 20:19:16]

I'm going to remove the comment now that it always returns non-null.

+  virtual std::unique_ptr<WorkspaceEventHandler> CreateWorkspaceEventHandler(
+      WmWindow* workspace_window) = 0;
+
   virtual std::unique_ptr<ScopedDisableInternalMouseAndKeyboard>
   CreateScopedDisableInternalMouseAndKeyboard() = 0;