SurfaceFlinger: Change to support framebuffer flip for 2D blitters

- Surfaceflinger does not flip framebuffers when there are
  no layers marked for HWC_FRAMEBUFFER
- This change checks for the HWC_BLIT flag and will request a flip
  to a new FB_TARGET buffer even if there are no FRAMEBUFFER layers

Conflicts:
	services/surfaceflinger/DisplayHardware/HWComposer.cpp
	services/surfaceflinger/Layer.cpp

Change-Id: I1cb44389a05c9ec049d7f0d39c288feccb11a91c
diff --git a/services/surfaceflinger/SurfaceFlinger.cpp b/services/surfaceflinger/SurfaceFlinger.cpp
index 0ff26be..c7567bd 100644
--- a/services/surfaceflinger/SurfaceFlinger.cpp
+++ b/services/surfaceflinger/SurfaceFlinger.cpp
@@ -1902,6 +1902,9 @@
                         layer->draw(hw, clip);
                         break;
                     }
+                    case HWC_BLIT:
+                        //Do nothing
+                        break;
                     case HWC_FRAMEBUFFER_TARGET: {
                         // this should not happen as the iterator shouldn't
                         // let us get there.