Move OpenGL specific details behind renderPipeline interface.

Test: new and existing unit tests still pass.
Change-Id: I6164f30f45ebe450788ed8d949eca5af9a44e585
diff --git a/libs/hwui/renderthread/RenderThread.h b/libs/hwui/renderthread/RenderThread.h
index c914098..d8677e13 100644
--- a/libs/hwui/renderthread/RenderThread.h
+++ b/libs/hwui/renderthread/RenderThread.h
@@ -89,8 +89,8 @@
     void pushBackFrameCallback(IFrameCallback* callback);
 
     TimeLord& timeLord() { return mTimeLord; }
-    RenderState& renderState() { return *mRenderState; }
-    EglManager& eglManager() { return *mEglManager; }
+    RenderState& renderState() const { return *mRenderState; }
+    EglManager& eglManager() const { return *mEglManager; }
     JankTracker& jankTracker() { return *mJankTracker; }
 
     const DisplayInfo& mainDisplayInfo() { return mDisplayInfo; }