Mark isInUse per-window

Bug: 22509159
Change-Id: I0ae0f1fa582ee38dcb9f24ca20f0b4d0c57ccb32
diff --git a/libs/hwui/TreeInfo.h b/libs/hwui/TreeInfo.h
index 0799c6c..ed853f7 100644
--- a/libs/hwui/TreeInfo.h
+++ b/libs/hwui/TreeInfo.h
@@ -95,7 +95,7 @@
     // layer updates or similar. May be NULL.
     OpenGLRenderer* renderer;
     ErrorHandler* errorHandler;
-    // TODO: Remove this? May be NULL
+    // May be NULL (TODO: can it really?)
     renderthread::CanvasContext* canvasContext;
 
     struct Out {