rename mInvalidRegion to mSwapRegion

Change-Id: I946cbc782c0c84645843ea44c3d8b04a0a2fe658
diff --git a/services/surfaceflinger/SurfaceFlinger.h b/services/surfaceflinger/SurfaceFlinger.h
index 126ca39..a8036a6 100644
--- a/services/surfaceflinger/SurfaceFlinger.h
+++ b/services/surfaceflinger/SurfaceFlinger.h
@@ -358,7 +358,7 @@
                 State                       mDrawingState;
                 Region                      mDirtyRegion;
                 Region                      mDirtyRegionRemovedLayer;
-                Region                      mInvalidRegion;
+                Region                      mSwapRegion;
                 Region                      mWormholeRegion;
                 bool                        mVisibleRegionsDirty;
                 bool                        mHwWorkListDirty;