Add method to create a ParcelSurfaceTexture from android.view.Surface.

Change-Id: I05e343ab7e327478f60322af9373574b70c148f5
diff --git a/libs/gui/Surface.cpp b/libs/gui/Surface.cpp
index 4d1d923..9185e1e 100644
--- a/libs/gui/Surface.cpp
+++ b/libs/gui/Surface.cpp
@@ -421,6 +421,10 @@
     return NO_ERROR;
 }
 
+sp<ISurfaceTexture> Surface::getSurfaceTexture() {
+    return mSurface != NULL ? mSurface->getSurfaceTexture() : NULL;
+}
+
 sp<IBinder> Surface::asBinder() const {
     return mSurface!=0 ? mSurface->asBinder() : 0;
 }