Make some SpdyStream methods const.

Some SpdyStream methods are conceptually const, mark them as such.

Change-Id: I89935beec587771045554e30dffdb998195e5e64
Reviewed-on: https://chromium-review.googlesource.com/1050190Reviewed-by: Ryan Hamilton <rch@chromium.org>
Commit-Queue: Bence Béky <bnc@chromium.org>
Cr-Commit-Position: refs/heads/master@{#557500}

net/spdy/chromium/spdy_stream.cc

@@ -470,7 +470,7 @@ void SpdyStream::OnHeadersReceived(const SpdyHeaderBlock& response_headers,
   }
 }
 
-bool SpdyStream::ShouldRetryRSTPushStream() {
+bool SpdyStream::ShouldRetryRSTPushStream() const {
   // Retry if the stream is a pushed stream, has been claimed, but did not yet
   // receive response headers
   return (response_headers_.empty() && type_ == SPDY_PUSH_STREAM && delegate_);

net/spdy/chromium/spdy_stream.h

@@ -387,12 +387,12 @@ class NET_EXPORT_PRIVATE SpdyStream {
   int64_t raw_received_bytes() const { return raw_received_bytes_; }
   int64_t raw_sent_bytes() const { return raw_sent_bytes_; }
   int recv_bytes() const { return recv_bytes_; }
-  bool ShouldRetryRSTPushStream();
+  bool ShouldRetryRSTPushStream() const;
 
   bool GetLoadTimingInfo(LoadTimingInfo* load_timing_info) const;
 
-  const SpdyHeaderBlock& request_headers() { return request_headers_; }
-  const SpdyHeaderBlock& response_headers() { return response_headers_; }
+  const SpdyHeaderBlock& request_headers() const { return request_headers_; }
+  const SpdyHeaderBlock& response_headers() const { return response_headers_; }
 
   // Returns the estimate of dynamically allocated memory in bytes.
   size_t EstimateMemoryUsage() const;