Adds UMA to measure when the data reduction proxy via header is missing

components/data_reduction_proxy/browser/data_reduction_proxy_usage_stats.h

Index: components/data_reduction_proxy/browser/data_reduction_proxy_usage_stats.h
diff --git a/components/data_reduction_proxy/browser/data_reduction_proxy_usage_stats.h b/components/data_reduction_proxy/browser/data_reduction_proxy_usage_stats.h
index 33fd29e560fa2f533fa044f1c3be60a83537c599..141335baa7577fb6089635ac5e44596750a32cab 100644
--- a/components/data_reduction_proxy/browser/data_reduction_proxy_usage_stats.h
+++ b/components/data_reduction_proxy/browser/data_reduction_proxy_usage_stats.h
@@ -17,6 +17,7 @@
 
 namespace net {
 class ProxyServer;
+class HttpResponseHeaders;
 }
 
 namespace data_reduction_proxy {
@@ -33,6 +34,12 @@ class DataReductionProxyUsageStats
       const net::ProxyServer& proxy_server,
       DataReductionProxyBypassType bypass_type);
 
+  // For the given response |headers| that are expected to include the data
+  // reduction proxy via header, records response code UMA if the data reduction
+  // proxy via header is not present.
+  static void DetectAndRecordMissingViaHeaderResponseCode(
+      bool is_primary, const net::HttpResponseHeaders* headers);
+
   // MessageLoopProxy instance is owned by io_thread. |params| outlives
   // this class instance.
   DataReductionProxyUsageStats(DataReductionProxyParams* params,
@@ -67,6 +74,11 @@ class DataReductionProxyUsageStats
   void RecordBypassEventHistograms(const net::ProxyServer& bypassed_proxy,
                                    int net_error) const;
 
+  // Records UMA of the number of response bytes of responses that are expected
+  // to have the data reduction proxy via header, but where the data reduction
+  // proxy via header is not present.
+  void RecordMissingViaHeaderBytes(net::URLRequest* request);
+
  private:
   enum BypassedBytesType {
     NOT_BYPASSED = 0,         /* Not bypassed. */