Android: Add scoped local ref. handler.

Adds an internal class for handling local jni references. When calling
raw jni functions the returned object is usually a local reference, to
avoid overflowing the local reference table we need to free any local
ref. as soon as we're done with them. The class QJNIScopedLocalRef,
a QScopedPointer, makes this process a lot easier.

Change-Id: I093e5671f0dcd254d5c2c7985c8c0f625d5592a4
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@theqtcompany.com>

src/corelib/kernel/qjni.cpp

@@ -204,6 +204,15 @@ static jfieldID getCachedFieldID(JNIEnv *env,
     }
 }
 
+void QJNILocalRefDeleter::cleanup(jobject obj)
+{
+    if (obj == 0)
+        return;
+
+    QJNIEnvironmentPrivate env;
+    env->DeleteLocalRef(obj);
+}
+
 class QJNIEnvironmentPrivateTLS
 {
 public:
@@ -2258,4 +2267,3 @@ bool QJNIObjectPrivate::isSameObject(const QJNIObjectPrivate &other) const
 }
 
 QT_END_NAMESPACE
-

src/corelib/kernel/qjni_p.h

@@ -51,6 +51,14 @@
 
 QT_BEGIN_NAMESPACE
 
+struct Q_CORE_EXPORT QJNILocalRefDeleter
+{
+    static void cleanup(jobject obj);
+};
+
+// To simplify this we only define it for jobjects.
+typedef QScopedPointer<_jobject, QJNILocalRefDeleter> QJNIScopedLocalRef;
+
 class Q_CORE_EXPORT QJNIEnvironmentPrivate
 {
 public: