[DO NOT REVIEW][DO NOT COMMIT] Implement WebDataProducerHandleImpl.

content/child/web_data_consumer_handle_impl.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 "content/child/web_data_consumer_handle_impl.h"
 
 #include <limits>
 #include "base/bind.h"
 #include "base/logging.h"
 #include "mojo/public/c/system/types.h"
@@ skipping 61 matching lines @@
 
   handle_watcher_.Start(
       handle_.get(),
       MOJO_HANDLE_SIGNAL_READABLE,
       MOJO_DEADLINE_INDEFINITE,
       base::Bind(&WebDataConsumerHandleImpl::OnHandleGotReadable,
                  base::Unretained(this)));
 }
 
 void WebDataConsumerHandleImpl::unregisterClient() {
+  DCHECK(client_);
   client_ = nullptr;
   handle_watcher_.Stop();
 }
 
 Result WebDataConsumerHandleImpl::HandleReadResult(MojoResult mojo_result) {
   switch (mojo_result) {
     case MOJO_RESULT_OK:
       return Ok;
     case MOJO_RESULT_FAILED_PRECONDITION:
       return Done;
@@ skipping 15 matching lines @@
       return UnexpectedError;
   }
 }
 
 void WebDataConsumerHandleImpl::OnHandleGotReadable(MojoResult) {
   DCHECK(client_);
   client_->didGetReadable();
 }
 
 }  // namespace content