hwc: Enable swapRect for overlapping use-cases

Use swapRect feature for use-cases with one updating layer
and updating layer is overlapping with other layers

Change-Id: I1a48926c941ef3e8184e1a6f80134f4e688741eb
diff --git a/libhwcomposer/hwc_copybit.h b/libhwcomposer/hwc_copybit.h
index a7ce43e..61f24ef 100644
--- a/libhwcomposer/hwc_copybit.h
+++ b/libhwcomposer/hwc_copybit.h
@@ -129,6 +129,7 @@
     int mDirtyLayerIndex;
     LayerCache mLayerCache;
     FbCache mFbCache;
+    hwc_rect_t mDirtyRect;
     int getLayersChanging(hwc_context_t *ctx, hwc_display_contents_1_t *list,
                   int dpy);
     int checkDirtyRect(hwc_context_t *ctx, hwc_display_contents_1_t *list,