Use default visibility for Snapshot::getLocalClip.

The method is in libhwui.so but used by libandroid_runtime.so
(via android_view_GLES20Canvas.cpp). If the compiler decides not to
inline this method, the linker won't be able to resolve the dependency
when it has hidden visibility.

The problem is found when testing GCC 4.9.

Change-Id: I3b4d096c7767f0bef0796886dfb2c5ba2ecff48c