Makes ash/wm/common a library

ash/wm/common/root_window_finder.cc

Index: ash/wm/common/root_window_finder.cc
diff --git a/ash/wm/common/root_window_finder.cc b/ash/wm/common/root_window_finder.cc
index 9be6c9052f62664628ca8f1a320335c93344e2cd..eb2cead1f110a1d0b92e9634792214c1916d6050 100644
--- a/ash/wm/common/root_window_finder.cc
+++ b/ash/wm/common/root_window_finder.cc
@@ -4,6 +4,7 @@
 
 #include "ash/wm/common/root_window_finder.h"
 
+#include "ash/wm/common/wm_lookup.h"
 #include "ash/wm/common/wm_root_window_controller.h"
 #include "ash/wm/common/wm_window.h"
 #include "ui/display/display.h"
@@ -19,7 +20,7 @@ WmWindow* GetRootWindowAt(const gfx::Point& point) {
       display::Screen::GetScreen()->GetDisplayNearestPoint(point);
   DCHECK(display.is_valid());
   WmRootWindowController* root_window_controller =
-      WmRootWindowController::GetWithDisplayId(display.id());
+      WmLookup::Get()->GetRootWindowControllerWithDisplayId(display.id());
   return root_window_controller ? root_window_controller->GetWindow() : nullptr;
 }
 
@@ -27,7 +28,7 @@ WmWindow* GetRootWindowMatching(const gfx::Rect& rect) {
   const display::Display& display =
       display::Screen::GetScreen()->GetDisplayMatching(rect);
   WmRootWindowController* root_window_controller =
-      WmRootWindowController::GetWithDisplayId(display.id());
+      WmLookup::Get()->GetRootWindowControllerWithDisplayId(display.id());
   return root_window_controller ? root_window_controller->GetWindow() : nullptr;
 }