Clear FBO cache on full memory flush

Change-Id: I44e06d5d15cd899a0522c62d7c0d042170665abb
diff --git a/libs/hwui/Caches.cpp b/libs/hwui/Caches.cpp
index df966e1..641cbc8 100644
--- a/libs/hwui/Caches.cpp
+++ b/libs/hwui/Caches.cpp
@@ -338,6 +338,7 @@
             dropShadowCache.clear();
             gradientCache.clear();
             fontRenderer->clear();
+            fboCache.clear();
             dither.clear();
             // fall through
         case kFlushMode_Moderate: