diff --git a/common/mock_http_fetcher.cc b/common/mock_http_fetcher.cc
index d0348f1..f1ae72a 100644
--- a/common/mock_http_fetcher.cc
+++ b/common/mock_http_fetcher.cc
@@ -123,6 +123,13 @@
   extra_headers_[base::ToLowerASCII(header_name)] = header_value;
 }
 
+std::string MockHttpFetcher::GetHeader(const std::string& header_name) const {
+  const auto it = extra_headers_.find(base::ToLowerASCII(header_name));
+  if (it == extra_headers_.end())
+    return "";
+  return it->second;
+}
+
 void MockHttpFetcher::Pause() {
   CHECK(!paused_);
   paused_ = true;
diff --git a/common/mock_http_fetcher.h b/common/mock_http_fetcher.h
index e56318e..367802e 100644
--- a/common/mock_http_fetcher.h
+++ b/common/mock_http_fetcher.h
@@ -91,6 +91,10 @@
   void SetHeader(const std::string& header_name,
                  const std::string& header_value) override;
 
+  // Return the value of the header |header_name| or the empty string if not
+  // set.
+  std::string GetHeader(const std::string& header_name) const;
+
   // Suspend the mock transfer.
   void Pause() override;