Update the mod_pagespeed histogram to be a sparse histogram.

chrome/browser/prerender/prerender_util.cc

 // Copyright (c) 2011 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 "chrome/browser/prerender/prerender_util.h"
 
 #include "base/logging.h"
-#include "base/metrics/histogram.h"
+#include "base/metrics/sparse_histogram.h"
 #include "base/strings/string_util.h"
 #include "content/public/browser/resource_request_info.h"
 #include "googleurl/src/url_canon.h"
 #include "googleurl/src/url_parse.h"
 #include "googleurl/src/url_util.h"
 #include "net/http/http_response_headers.h"
 #include "net/url_request/url_request.h"
 
 namespace prerender {
 
@@ skipping 75 matching lines @@
 }
 
 void URLRequestResponseStarted(net::URLRequest* request) {
   static const char* kModPagespeedHeader = "X-Mod-Pagespeed";
   static const char* kModPagespeedHistogram = "Prerender.ModPagespeedHeader";
   const content::ResourceRequestInfo* info =
       content::ResourceRequestInfo::ForRequest(request);
   // Gather histogram information about the X-Mod-Pagespeed header.
   if (info->GetResourceType() == ResourceType::MAIN_FRAME &&
       IsWebURL(request->url())) {
-    UMA_HISTOGRAM_ENUMERATION(kModPagespeedHistogram, 0, 101);
+    UMA_HISTOGRAM_SPARSE_SLOWLY(kModPagespeedHistogram, 0);
     if (request->response_headers() &&
         request->response_headers()->HasHeader(kModPagespeedHeader)) {
-      UMA_HISTOGRAM_ENUMERATION(kModPagespeedHistogram, 1, 101);
+      UMA_HISTOGRAM_SPARSE_SLOWLY(kModPagespeedHistogram, 1);
 
       // Attempt to parse the version number, and encode it in buckets
       // 2 through 99. 0 and 1 are used to store all pageviews and
       // # pageviews with the MPS header (see above).
       void* iter = NULL;
       std::string mps_version;
       if (request->response_headers()->EnumerateHeader(
               &iter, kModPagespeedHeader, &mps_version) &&
           !mps_version.empty()) {
         // Mod Pagespeed versions are of the form a.b.c.d-e
         int a, b, c, d, e;
         int num_parsed = sscanf(mps_version.c_str(), "%d.%d.%d.%d-%d",
                                 &a, &b, &c, &d, &e);
         if (num_parsed == 5) {
           int output = 2;
           if (c > 10)
             output += 2 * (c - 10);
           if (d > 1)
             output++;
           if (output < 2 || output >= 99)
             output = 99;
-          UMA_HISTOGRAM_ENUMERATION(kModPagespeedHistogram, output, 101);
+          UMA_HISTOGRAM_SPARSE_SLOWLY(kModPagespeedHistogram, output);
         }
       }
     }
   }
 }
 
 }  // namespace prerender