Yet more layer tracking logging

 Bug: 17208461

Change-Id: I55e7d0921eb565867e966d68b798b7b92c391b55
diff --git a/libs/hwui/renderthread/RenderThread.h b/libs/hwui/renderthread/RenderThread.h
index 0b91e9d..c461f3a 100644
--- a/libs/hwui/renderthread/RenderThread.h
+++ b/libs/hwui/renderthread/RenderThread.h
@@ -40,6 +40,7 @@
 
 namespace renderthread {
 
+class CanvasContext;
 class DispatchFrameCallbacks;
 class EglManager;
 class RenderProxy;