Optimize saveLayer() when the clip flag is set.

This speeds up applications, especially Launcher.
diff --git a/libs/hwui/LayerCache.h b/libs/hwui/LayerCache.h
index c0c7542..cbb7ae2 100644
--- a/libs/hwui/LayerCache.h
+++ b/libs/hwui/LayerCache.h
@@ -64,6 +64,7 @@
      * @param size The dimensions of the desired layer
      */
     Layer* get(LayerSize& size);
+
     /**
      * Adds the layer to the cache. The layer will not be added if there is
      * not enough space available.
@@ -96,7 +97,6 @@
     void deleteLayer(Layer* layer);
 
     GenerationCache<LayerSize, Layer*> mCache;
-    uint32_t mIdGenerator;
 
     uint32_t mSize;
     uint32_t mMaxSize;