am 17ef62cc: fix a possible dead-lock when clearing caches

    textureCache.clearGarbage();

    pathCache.clearGarbage();

    Vector<DisplayList*> displayLists;

    Vector<Layer*> layers;

    { // scope for the lock

        Mutex::Autolock _l(mGarbageLock);

        displayLists = mDisplayListGarbage;

        layers = mLayerGarbage;

        mDisplayListGarbage.clear();

        mLayerGarbage.clear();

    }

    size_t count = mLayerGarbage.size();

    size_t count = displayLists.size();

    for (size_t i = 0; i < count; i++) {

        Layer* layer = mLayerGarbage.itemAt(i);

        delete layer;

        DisplayList* displayList = displayLists.itemAt(i);

        delete displayList;

    }

    mLayerGarbage.clear();

    count = mDisplayListGarbage.size();

    count = layers.size();

    for (size_t i = 0; i < count; i++) {

        DisplayList* displayList = mDisplayListGarbage.itemAt(i);

        delete displayList;

        Layer* layer = layers.itemAt(i);

        delete layer;

    }

    mDisplayListGarbage.clear();

    layers.clear();

}

void Caches::deleteLayerDeferred(Layer* layer) {