make transform hint multi-display aware

if a layer is not mirrored, we now use its display
as the source for the transfrom hint calculation
instead of always using the default (main) display.

this change does two thing:
1) we make updateTransformHint take a DisplayDevice
   as a parameter instead of hard-coding the
   main display.

2) each time we do a transaction that could change
   the hint, we go through all layers and
   figure out which display should be used for their
   transform hint.

Bug: 7599344
Change-Id: I9b04a95e6c372dd770bacf81d8ef6f8e31b87b83
diff --git a/services/surfaceflinger/LayerBase.h b/services/surfaceflinger/LayerBase.h
index 00c4ffe..4d5a5b0 100644
--- a/services/surfaceflinger/LayerBase.h
+++ b/services/surfaceflinger/LayerBase.h
@@ -246,7 +246,7 @@
      * Updates the SurfaceTexture's transform hint, for layers that have
      * a SurfaceTexture.
      */
-    virtual void updateTransformHint() const { }
+    virtual void updateTransformHint(const sp<const DisplayDevice>& hw) const { }
 
     /** always call base class first */
     virtual void dump(String8& result, char* scratch, size_t size) const;