Add a helper to get the referent of a Reference.

Change-Id: I8ac5a69fab563e220d48c94e254f5ed3055abe5f
diff --git a/include/nativehelper/JNIHelp.h b/include/nativehelper/JNIHelp.h
index 446a710..2fadcdf 100644
--- a/include/nativehelper/JNIHelp.h
+++ b/include/nativehelper/JNIHelp.h
@@ -97,6 +97,11 @@
 void jniSetFileDescriptorOfFD(C_JNIEnv* env, jobject fileDescriptor, int value);
 
 /*
+ * Returns the reference from a java.lang.ref.Reference.
+ */
+jobject jniGetReferent(C_JNIEnv* env, jobject ref);
+
+/*
  * Log a message and an exception.
  * If exception is NULL, logs the current exception in the JNI environment.
  */
@@ -157,6 +162,10 @@
     jniSetFileDescriptorOfFD(&env->functions, fileDescriptor, value);
 }
 
+inline jobject jniGetReferent(JNIEnv* env, jobject ref) {
+    return jniGetReferent(&env->functions, ref);
+}
+
 inline void jniLogException(JNIEnv* env, int priority, const char* tag, jthrowable exception = NULL) {
     jniLogException(&env->functions, priority, tag, exception);
 }