SF: Use getVisibleLayers... in doComposeSurfaces

in b/114101122, it is discovered that there is a problem
in indexing the SF mCompositionInfo by displayId because
there are multiple displays that have the same id (-1).

This change uses getVisibleLayersSortedByZ in doComposeSurfaces
until we can fix the indexing of mCompositionInfo.

Bug: 114101122
Test: run cts -m CtsViewTestCases, CtsMediaTestCases

Change-Id: I90adb957c183400c396f25fa9583b668e1da8417
diff --git a/services/surfaceflinger/LayerBE.h b/services/surfaceflinger/LayerBE.h
index f5150a7..a8bdec4 100644
--- a/services/surfaceflinger/LayerBE.h
+++ b/services/surfaceflinger/LayerBE.h
@@ -94,8 +94,8 @@
     void clear(renderengine::RenderEngine& renderEngine);
     renderengine::Mesh& getMesh() { return mMesh; }
 
-private:
     Layer*const mLayer;
+private:
     // The mesh used to draw the layer in GLES composition mode
     renderengine::Mesh mMesh;