surfaceflinger: add support for gralloc dump hooks

Change-Id: Ib6f539ed0132b70d040d653c03d52cc04249ac3c
diff --git a/services/surfaceflinger/DisplayHardware/DisplayHardware.h b/services/surfaceflinger/DisplayHardware/DisplayHardware.h
index 75b55df..eb71e8b 100644
--- a/services/surfaceflinger/DisplayHardware/DisplayHardware.h
+++ b/services/surfaceflinger/DisplayHardware/DisplayHardware.h
@@ -80,6 +80,8 @@
     EGLDisplay getEGLDisplay() const { return mDisplay; }
     overlay_control_device_t* getOverlayEngine() const { return mOverlayEngine; }
 
+    void dump(String8& res) const;
+
     // Hardware Composer
     HWComposer& getHwComposer() const;