Allow ~Layer() to happen after onGLContextDestroyed

Bug: 19146354
Change-Id: I9e885936168bd541bfbed4064ad67ab524f58e32
diff --git a/libs/hwui/Caches.cpp b/libs/hwui/Caches.cpp
index 4bbe6ed..cdf8150 100644
--- a/libs/hwui/Caches.cpp
+++ b/libs/hwui/Caches.cpp
@@ -273,7 +273,7 @@
             layerCache.getSize(), layerCache.getMaxSize(), layerCache.getCount());
     if (mRenderState) {
         int memused = 0;
-        for (std::set<const Layer*>::iterator it = mRenderState->mActiveLayers.begin();
+        for (std::set<Layer*>::iterator it = mRenderState->mActiveLayers.begin();
                 it != mRenderState->mActiveLayers.end(); it++) {
             const Layer* layer = *it;
             log.appendFormat("    Layer size %dx%d; isTextureLayer()=%d; texid=%u fbo=%u; refs=%d\n",