Remove default traffic annotation value from 2 classes.

The default network traffic annotation value is removed from the Write
function of the following classes:
 - HttpProxyClientSocket
 - HttpProxyClientSocketWrapper

Bug: 656607
Change-Id: Iae5bb59c2391504e457a323fa178673d70676696
Reviewed-on: https://chromium-review.googlesource.com/817416Reviewed-by: Eric Roman <eroman@chromium.org>
Commit-Queue: Ramin Halavati <rhalavati@chromium.org>
Cr-Commit-Position: refs/heads/master@{#523351}

net/http/http_proxy_client_socket.h

@@ -82,12 +82,10 @@ class NET_EXPORT_PRIVATE HttpProxyClientSocket : public ProxyClientSocket {
   int Read(IOBuffer* buf,
            int buf_len,
            const CompletionCallback& callback) override;
-  // TODO(crbug.com/656607): Remove default value.
   int Write(IOBuffer* buf,
             int buf_len,
             const CompletionCallback& callback,
-            const NetworkTrafficAnnotationTag& traffic_annotation =
-                NO_TRAFFIC_ANNOTATION_BUG_656607) override;
+            const NetworkTrafficAnnotationTag& traffic_annotation) override;
   int SetReceiveBufferSize(int32_t size) override;
   int SetSendBufferSize(int32_t size) override;
   int GetPeerAddress(IPEndPoint* address) const override;

net/http/http_proxy_client_socket_wrapper.h

@@ -114,12 +114,10 @@ class NET_EXPORT_PRIVATE HttpProxyClientSocketWrapper
   int Read(IOBuffer* buf,
            int buf_len,
            const CompletionCallback& callback) override;
-  // TODO(crbug.com/656607): Remove default value.
   int Write(IOBuffer* buf,
             int buf_len,
             const CompletionCallback& callback,
-            const NetworkTrafficAnnotationTag& traffic_annotation =
-                NO_TRAFFIC_ANNOTATION_BUG_656607) override;
+            const NetworkTrafficAnnotationTag& traffic_annotation) override;
   int SetReceiveBufferSize(int32_t size) override;
   int SetSendBufferSize(int32_t size) override;
   int GetPeerAddress(IPEndPoint* address) const override;