SF: Decouple MessageQueue

Define an ICompositor interface against which MessageQueue (which ought
to be an implementation detail of Scheduler) is implemented. Change the
equivocal invalidate/refresh nomenclature to commit/composite. Schedule
sampling only after composite.

Bug: 185535769
Test: libsurfaceflinger_unittest
Change-Id: I0c18f312459bae48531449f24f7b53c104fc5812
diff --git a/services/surfaceflinger/BufferLayer.cpp b/services/surfaceflinger/BufferLayer.cpp
index ef05fe2..160b2ea 100644
--- a/services/surfaceflinger/BufferLayer.cpp
+++ b/services/surfaceflinger/BufferLayer.cpp
@@ -486,7 +486,7 @@
     // try again later
     if (!fenceHasSignaled()) {
         ATRACE_NAME("!fenceHasSignaled()");
-        mFlinger->signalLayerUpdate();
+        mFlinger->onLayerUpdate();
         return false;
     }