jni: is loggable speedup, not within signal

Speedup by telling __android_is_loggable interface it will not
be called within a signal handler. This saves two system calls.

Bug: 25563384
Change-Id: Ib8188641c8c76e5aa848476da98596be6b8e5040

core/jni/android_util_Log.cpp

@@ -42,7 +42,9 @@ struct levels_t {
 static levels_t levels;
 
 static jboolean isLoggable(const char* tag, jint level) {
-    return __android_log_is_loggable(level, tag, ANDROID_LOG_INFO);
+    return __android_log_is_loggable(level, tag,
+                                     ANDROID_LOG_INFO |
+                                     ANDROID_LOGGABLE_FLAG_NOT_WITHIN_SIGNAL);
 }
 
 static jboolean android_util_Log_isLoggable(JNIEnv* env, jobject clazz, jstring tag, jint level)