Add DISALLOW_COPY_AND_ASSIGN macro.

Make the DISALLOW_COPY_AND_ASSIGN macro delete the member functions rather
than just not defining them to improve analysis of the Scoped.. classes.
Add a few missing const qualifiers.

Change-Id: I48eee0c22908d45a05df6979aa61442d2eedcf36
diff --git a/JNIHelp.cpp b/JNIHelp.cpp
index 9de3dfc..49c4f94 100644
--- a/JNIHelp.cpp
+++ b/JNIHelp.cpp
@@ -59,12 +59,10 @@
     }
 
 private:
-    C_JNIEnv* mEnv;
+    C_JNIEnv* const mEnv;
     T mLocalRef;
 
-    // Disallow copy and assignment.
-    scoped_local_ref(const scoped_local_ref&);
-    void operator=(const scoped_local_ref&);
+    DISALLOW_COPY_AND_ASSIGN(scoped_local_ref);
 };
 
 static jclass findClass(C_JNIEnv* env, const char* className) {