Geolocation: log the number of wifi access points used to determine location.

content/browser/geolocation/network_location_request.cc

 // Copyright (c) 2012 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 "content/browser/geolocation/network_location_request.h"
 
 #include <set>
 #include <string>
 
 #include "base/json/json_reader.h"
@@ skipping 40 matching lines @@
 void RecordUmaEvent(NetworkLocationRequestEvent event) {
   UMA_HISTOGRAM_ENUMERATION("Geolocation.NetworkLocationRequest.Event",
       event, NETWORK_LOCATION_REQUEST_EVENT_COUNT);
 }
 
 void RecordUmaResponseCode(int code) {
   UMA_HISTOGRAM_SPARSE_SLOWLY("Geolocation.NetworkLocationRequest.ResponseCode",
       code);
 }
 
+void RecordUmaAccessPoints(int count) {
+  UMA_HISTOGRAM_SPARSE_SLOWLY("Geolocation.NetworkLocationRequest.AccessPoints",
+      count);

[Ilya Sherman, 2013/10/08 23:51:03]

What sorts of counts are expected?  Could you use a non-sparse histogram
instead?  A sparse histogram is likely to be less efficient for this use-case
than something like UMA_HISTOGRAM_COUNTS.

[Michael van Ouwerkerk, 2013/10/09 13:09:57]

I expect counts of 0 to 10 but in some cases there will be more. I want to use
buckets of size 1 for the range of 0 - 10.

I shied away from the macros in histogram.h because the comments state 0 is not
a possible value, it will be silently clamped to 1. Is this actually true?

[Ilya Sherman, 2013/10/09 22:47:40]

I'm pretty sure this is not accurate -- 0 is a valid bucket.  It's also the
implicit underflow bucket, but that shouldn't be an issue for this histogram. 
You can double-check this locally by emitting a 0 to the histogram, and then
navigate to chrome:histograms to see what values the histogram has.

[Michael van Ouwerkerk, 2013/10/10 10:20:03]

Done.

+}
+
 // Local functions
 // Creates the request url to send to the server.
 GURL FormRequestURL(const GURL& url);
 
 void FormUploadData(const WifiData& wifi_data,
                     const base::Time& timestamp,
                     const string16& access_token,
                     std::string* upload_data);
 
 // Attempts to extract a position from the response. Detects and indicates
@@ skipping 29 matching lines @@
           url_(url) {
 }
 
 NetworkLocationRequest::~NetworkLocationRequest() {
 }
 
 bool NetworkLocationRequest::MakeRequest(const string16& access_token,
                                          const WifiData& wifi_data,
                                          const base::Time& timestamp) {
   RecordUmaEvent(NETWORK_LOCATION_REQUEST_EVENT_REQUEST_START);
+  RecordUmaAccessPoints(wifi_data.access_point_data.size());
   if (url_fetcher_ != NULL) {
     DVLOG(1) << "NetworkLocationRequest : Cancelling pending request";
     RecordUmaEvent(NETWORK_LOCATION_REQUEST_EVENT_REQUEST_CANCEL);
     url_fetcher_.reset();
   }
   wifi_data_ = wifi_data;
   timestamp_ = timestamp;
 
   GURL request_url = FormRequestURL(url_);
   url_fetcher_.reset(net::URLFetcher::Create(
@@ skipping 293 matching lines @@
 
   // Other fields are optional.
   GetAsDouble(*response_object, kAccuracyString, &position->accuracy);
 
   return true;
 }
 
 }  // namespace
 
 }  // namespace content