Frameworks/base: Consistency in core/jni

Make consistent use of core_jni_helpers for registration.

Translate some #ifdefs into const bools.

Change-Id: I37639aa053dd50f003a552cbd8550dddecc811c5
diff --git a/core/jni/Android.mk b/core/jni/Android.mk
index d53a5b80..97e0fd3 100644
--- a/core/jni/Android.mk
+++ b/core/jni/Android.mk
@@ -265,6 +265,10 @@
 #                       off a GCC warning that Clang doesn't know.
 LOCAL_CFLAGS += -Wall -Werror -Wunused -Wunreachable-code -Wno-unknown-pragmas
 
+# -Wno-c++11-extensions: Clang warns about Skia using the C++11 override keyword, but this project
+#                        is not being compiled with that level. Remove once this has changed.
+LOCAL_CFLAGS += -Wno-c++11-extensions
+
 include $(BUILD_SHARED_LIBRARY)
 
 include $(call all-makefiles-under,$(LOCAL_PATH))