MonitorManager to manage multiple monitors.

ash/shell.h

Index: ash/shell.h
diff --git a/ash/shell.h b/ash/shell.h
index e6af0db939fc28b2e00525c0cf7048cd2e9e680f..d2903757643b9b8b5ebeab4cb5230a26a3a9f8cf 100644
--- a/ash/shell.h
+++ b/ash/shell.h
@@ -156,8 +156,10 @@ class ASH_EXPORT Shell {
   // Rotate focus through containers that can receive focus.
   void RotateFocus(Direction direction);
 
-  // Sets the screen's work area insets, this notifies observers too.
-  void SetScreenWorkAreaInsets(const gfx::Insets& insets);
+  // Sets the work area insets of the monitor that contains |window|,
+  // this notifies observers too.
+  void SetMonitorWorkAreaInsets(aura::Window* window,
+                                const gfx::Insets& insets);
 
   // Add/remove observer.
   void AddShellObserver(ShellObserver* observer);