Fix warning

Bug: 21608208
Change-Id: I1d1cf1fbc8c0a4561bf76e307c56be580fb4baef
diff --git a/libs/hwui/FrameInfo.h b/libs/hwui/FrameInfo.h
index bcfae1b..38a6a21 100644
--- a/libs/hwui/FrameInfo.h
+++ b/libs/hwui/FrameInfo.h
@@ -50,7 +50,7 @@
     kNumIndexes
 };
 
-extern std::string FrameInfoNames[];
+extern const std::string FrameInfoNames[];
 
 enum class FrameInfoFlags {
     kWindowLayoutChanged = 1 << 0,