Modified SurfaceFlinger to implment setActiveConfig and getActiveConfig.

This can be used to change the current display mode of the device.

Change-Id: Icdc3fb58389b861dc77b68102083da6f7a96eccb
Tested: None
(cherry picked from commit 2651fa94635a96d653038fb389a0dd827338f8d3)
diff --git a/services/surfaceflinger/SurfaceFlinger.h b/services/surfaceflinger/SurfaceFlinger.h
index 476e549..5ae3d0b 100644
--- a/services/surfaceflinger/SurfaceFlinger.h
+++ b/services/surfaceflinger/SurfaceFlinger.h
@@ -239,6 +239,8 @@
 
     // called on the main thread in response to initializeDisplays()
     void onInitializeDisplays();
+    // called on the main thread in response to setActiveConfig()
+    void setActiveConfigInternal(const sp<DisplayDevice>& hw, int mode);
     // called on the main thread in response to setPowerMode()
     void setPowerModeInternal(const sp<DisplayDevice>& hw, int mode);