jni: Forbid inappropriate JNI parameter conversions.

base/android/scoped_java_ref.h

Index: base/android/scoped_java_ref.h
diff --git a/base/android/scoped_java_ref.h b/base/android/scoped_java_ref.h
index d6a81fa637f3b1214593f50d0a5d5e6989c42632..6d441954a4e902f0781a9f1bc54cd5a7bafeb87e 100644
--- a/base/android/scoped_java_ref.h
+++ b/base/android/scoped_java_ref.h
@@ -193,6 +193,13 @@ class ScopedJavaLocalRef : public JavaRef<T> {
   // This class is only good for use on the thread it was created on so
   // it's safe to cache the non-threadsafe JNIEnv* inside this object.
   JNIEnv* env_;
+
+  // Prevent ScopedJavaLocalRef(JNIEnv*, T obj) from being used to take
+  // ownership of a JavaParamRef's underlying object - parameters are not
+  // allowed to be deleted and so should not be owned by ScopedJavaLocalRef.
+  // TODO(torne): this can be removed once JavaParamRef no longer has an
+  // implicit conversion back to T.
+  ScopedJavaLocalRef(JNIEnv* env, const JavaParamRef<T>& other);
 };
 
 // Holds a global reference to a Java object. The global reference is scoped