mash: Add WmShell::SetDisplayWorkAreaInsets for ShelfLayoutManager.

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 790809a04ff5439e65cc8d56d170fc882ce10a30..02dbdfc40f7cc721b0dda0a0b84076c578c4344f 100644
--- a/ash/common/wm_shell.h
+++ b/ash/common/wm_shell.h
@@ -23,6 +23,7 @@ class Display;
 }
 
 namespace gfx {
+class Insets;
 class Point;
 }
 
@@ -188,6 +189,10 @@ class ASH_EXPORT WmShell {
   // the window size.
   virtual bool IsForceMaximizeOnFirstRun() = 0;
 
+  // Sets work area insets of the display containing |window|, pings observers.
+  virtual void SetDisplayWorkAreaInsets(WmWindow* window,
+                                        const gfx::Insets& insets) = 0;
+
   // Returns true if a system-modal dialog window is currently open.
   bool IsSystemModalWindowOpen();