Android: Generate JNI code for stats

This CL also unifies the functions for converting from C++ to Java, and
generates the boiler plate for converting C++ vectors to Java arrays.

Bug: webrtc:8278
Change-Id: I262e9162beae8a64ba0e8b6a27e1081207b03961
Reviewed-on: https://webrtc-review.googlesource.com/26020
Commit-Queue: Magnus Jedvert <magjed@webrtc.org>
Reviewed-by: Sami Kalliomäki <sakal@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20918}

sdk/android/api/org/webrtc/IceCandidate.java

@@ -49,9 +49,4 @@ public class IceCandidate {
   String getSdp() {
     return sdp;
   }
-
-  @CalledByNative
-  static IceCandidate[] createArray(int size) {
-    return new IceCandidate[size];
-  }
 }