libhardware: Add dirty region field to hwc layer

This change adds dirty region field to hwc_layer_1_t structure to
pass the layer's dirty region information since the previous frame.

Change-Id: I5b107b702636c6b1f662703a29dfda4793c02809
diff --git a/include/hardware/hwcomposer.h b/include/hardware/hwcomposer.h
index 3dfb4fd..4818d0b 100644
--- a/include/hardware/hwcomposer.h
+++ b/include/hardware/hwcomposer.h
@@ -215,6 +215,10 @@
              */
             hwc_region_t visibleRegionScreen;
 
+            /* Region of the layer changed in the source buffer since
+             * previous frame */
+            hwc_rect_t dirtyRect;
+
             /* Sync fence object that will be signaled when the buffer's
              * contents are available. May be -1 if the contents are already
              * available. This field is only valid during set(), and should be