Fix a pair of Cronet upload bugs and add tests.

components/cronet/android/wrapped_channel_upload_element_reader.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "components/cronet/android/wrapped_channel_upload_element_reader.h"
 
 #include "base/android/jni_android.h"
 #include "base/logging.h"
 #include "net/base/io_buffer.h"
 #include "net/base/net_errors.h"
 
 namespace cronet {
 
 WrappedChannelElementReader::WrappedChannelElementReader(
     scoped_refptr<URLRequestAdapter::URLRequestAdapterDelegate> delegate,
     uint64 length)
     : length_(length), offset_(0), delegate_(delegate) {
 }
 
 WrappedChannelElementReader::~WrappedChannelElementReader() {
 }
 
 int WrappedChannelElementReader::Init(const net::CompletionCallback& callback) {
-  offset_ = 0;
+  if (offset_ != 0)
+    return net::ERR_UPLOAD_STREAM_REWIND_NOT_SUPPORTED;
   return net::OK;
 }
 
 uint64 WrappedChannelElementReader::GetContentLength() const {
   return length_;
 }
 
 uint64 WrappedChannelElementReader::BytesRemaining() const {
   return length_ - offset_;
 }
@@ skipping 10 matching lines @@
   // TODO(mef): Post the read to file thread.
   int bytes_read = delegate_->ReadFromUploadChannel(buf, buf_length);
   if (bytes_read < 0)
     return net::ERR_FAILED;
   offset_ += bytes_read;
   return bytes_read;
 }
 
 }  // namespace cronet