don't hardcode "mSurface" throughout our source code

this is used in a few places to get access to the android.view.Surface
native surface. use a macro instead. Also rename the field to mNativeSurface.

Change-Id: I1c6dea14abd6b8b1392c7f97b304115999355094
diff --git a/include/surfaceflinger/Surface.h b/include/surfaceflinger/Surface.h
index 0279d84..4c8d023 100644
--- a/include/surfaceflinger/Surface.h
+++ b/include/surfaceflinger/Surface.h
@@ -30,6 +30,8 @@
 #include <surfaceflinger/ISurface.h>
 #include <surfaceflinger/ISurfaceFlingerClient.h>
 
+#define ANDROID_VIEW_SURFACE_JNI_ID    "mNativeSurface"
+
 namespace android {
 
 // ---------------------------------------------------------------------------