Remove explicit JNI references by adding UrlRequest.readFromUploadChannel callback.

components/cronet/android/url_request_peer.cc

Index: components/cronet/android/url_request_peer.cc
diff --git a/components/cronet/android/url_request_peer.cc b/components/cronet/android/url_request_peer.cc
index 8711f0ba709b6ff92997309e3141e3c83f542d66..5f413e60281ef8360d97c08a21a018d9242099f8 100644
--- a/components/cronet/android/url_request_peer.cc
+++ b/components/cronet/android/url_request_peer.cc
@@ -51,10 +51,9 @@ void URLRequestPeer::SetUploadContent(const char* bytes, int bytes_len) {
       reader.Pass(), 0));
 }
 
-void URLRequestPeer::SetUploadChannel(
-    JNIEnv* env, jobject channel, int64 content_length) {
+void URLRequestPeer::SetUploadChannel(JNIEnv* env, int64 content_length) {
   scoped_ptr<net::UploadElementReader> reader(
-      new WrappedChannelElementReader(env, channel, content_length));
+      new WrappedChannelElementReader(delegate_, content_length));
   upload_data_stream_.reset(net::UploadDataStream::CreateWithReader(
       reader.Pass(), 0));
 }