Destroy layers and flush layers cache when a window is destroyed.

Change-Id: I3fa1bc3ff50fb99e3d2e490925bd6b0a0f809fff
diff --git a/libs/hwui/Caches.cpp b/libs/hwui/Caches.cpp
index 7114b6a..c5858e9 100644
--- a/libs/hwui/Caches.cpp
+++ b/libs/hwui/Caches.cpp
@@ -173,13 +173,15 @@
             gradientCache.clear();
             // fall through
         case kFlushMode_Moderate:
-            layerCache.clear();
             pathCache.clear();
             roundRectShapeCache.clear();
             circleShapeCache.clear();
             ovalShapeCache.clear();
             rectShapeCache.clear();
             arcShapeCache.clear();
+            // fall through
+        case kFlushMode_Layers:
+            layerCache.clear();
             break;
     }
 }