Bug 1369992 - Make GetNative as public for clang. r=jolin

When building Fennec using clang, the following build error occurs.

 0:17.02 /mozilla/mobile/media/webrtc/signaling/src/media-conduit/WebrtcMediaCodecVP8VideoCodec.cpp:1099:27: error: 'GetNative' is a protected member of 'mozilla::jni::NativeImpl<mozilla::java::CodecProxy::NativeCallbacks, mozilla::JavaCallbacksSupport>'
 0:17.02     JavaCallbacksSupport::GetNative(mJavaCallbacks)->Cancel();
 0:17.02                           ^
 0:17.02 /mozilla/objdir-android/dist/include/mozilla/jni/Natives.h:821:18: note: declared protected here
 0:17.02     static Impl* GetNative(const typename Cls::LocalRef& instance) {
 0:17.02                  ^

We should define GetNative as public into JavaCallbacksSupport.h.

MozReview-Commit-ID: DYEyB2dRK8y

--HG--
extra : rebase_source : 8f77cac02800149aef814ce5fcd7bd3d23b56193

dom/media/platforms/android/JavaCallbacksSupport.h

@@ -17,6 +17,7 @@ class JavaCallbacksSupport
 public:
   typedef java::CodecProxy::NativeCallbacks::Natives<JavaCallbacksSupport> Base;
   using Base::AttachNative;
+  using Base::GetNative;
   using Base::DisposeNative;
 
   JavaCallbacksSupport() : mCanceled(false) { }