SF: Add onLayerDisplayed method to LayerBE

Add onLayerDisplayed method to LayerBE class and make the data
for the class private.

Merged-in: I2a5b03d542d46fc0c2e1d6d725fb87580980427d
Test: Compile/Run manually
Change-Id: I2a5b03d542d46fc0c2e1d6d725fb87580980427d
diff --git a/services/surfaceflinger/Android.bp b/services/surfaceflinger/Android.bp
index ff994f5..cba94d2 100644
--- a/services/surfaceflinger/Android.bp
+++ b/services/surfaceflinger/Android.bp
@@ -103,6 +103,7 @@
         "FrameTracker.cpp",
         "GpuService.cpp",
         "Layer.cpp",
+	"LayerBE.cpp",
         "LayerProtoHelper.cpp",
         "LayerRejecter.cpp",
         "LayerStats.cpp",