remove a dependency of DisplayDevice on the refresh rate

this remove a dependency (not all) on FramebufferSurface

Change-Id: Ie07ce70760cdcedfb41b5b41bea8da45637bf474
diff --git a/services/surfaceflinger/DisplayHardware/HWComposer.h b/services/surfaceflinger/DisplayHardware/HWComposer.h
index 872ab98..b9c9337 100644
--- a/services/surfaceflinger/DisplayHardware/HWComposer.h
+++ b/services/surfaceflinger/DisplayHardware/HWComposer.h
@@ -55,8 +55,7 @@
         virtual ~EventHandler() {}
     };
 
-    HWComposer(const sp<SurfaceFlinger>& flinger,
-            EventHandler& handler, nsecs_t refreshPeriod);
+    HWComposer(const sp<SurfaceFlinger>& flinger, EventHandler& handler);
     ~HWComposer();
 
     status_t initCheck() const;
@@ -189,6 +188,7 @@
 
     void eventControl(int event, int enabled);
 
+    nsecs_t getRefreshPeriod() const;
     nsecs_t getRefreshTimestamp() const;
 
     // this class is only used to fake the VSync event on systems that don't