[PageLoadMetrics] Record bytes usage per page

chrome/browser/page_load_metrics/observers/core_page_load_metrics_observer.cc

Index: chrome/browser/page_load_metrics/observers/core_page_load_metrics_observer.cc
diff --git a/chrome/browser/page_load_metrics/observers/core_page_load_metrics_observer.cc b/chrome/browser/page_load_metrics/observers/core_page_load_metrics_observer.cc
index 6d6e2b549f8819d2417dd310a9ac38e3f745634c..6baefbaaf5c55c9b0234563c76a508e0c9412111 100644
--- a/chrome/browser/page_load_metrics/observers/core_page_load_metrics_observer.cc
+++ b/chrome/browser/page_load_metrics/observers/core_page_load_metrics_observer.cc
@@ -203,6 +203,13 @@ const char kHistogramFirstNonScrollInputAfterFirstPaint[] =
 const char kHistogramFirstScrollInputAfterFirstPaint[] =
     "PageLoad.InputTiming.NavigationToFirstScroll.AfterPaint";
 
+const char kHistogramTotalBytesOnComplete[] =
+    "PageLoad.Experimental.Bytes.Total.OnComplete";
+const char kHistogramNetworkBytesOnComplete[] =
+    "PageLoad.Experimental.Bytes.Network.OnComplete";
+const char kHistogramCacheBytesOnComplete[] =
+    "PageLoad.Experimental.Bytes.Cache.OnComplete";
+
 }  // namespace internal
 
 CorePageLoadMetricsObserver::CorePageLoadMetricsObserver()
@@ -532,6 +539,20 @@ void CorePageLoadMetricsObserver::OnComplete(
     const page_load_metrics::PageLoadExtraInfo& info) {

[Bryan McQuade, 2016/12/16 14:28:45]

On Android, OnComplete doesn't get called about 1/3 of the time that the app
gets backgrounded, due to being killed while in the background. This leads to
data with some bias.

We can't address this perfectly, but a few things we can do to help us improve
our understanding:
1. you could implement the FlushMetricsOnAppEnterBackground callback, and log
bytes received up to that point in a separate histogram. I'm not totally sure
this addresses the issue, though. Is there something more complete we can do to
help us understand potential for bias?

2. We may also want to log bytes received up until the page goes into the
background by adding histograms in the OnHidden callback. That callback gets
invoked reliably for all page loads that are backgrounded.

[jkarlin, 2016/12/19 19:26:01]

ACK. I've added a comment about the Android bias in the base class OnComplete
docs. Mind if we add additional metrics in a followup however?

   RecordTimingHistograms(timing, info);
   RecordRappor(timing, info);
+
+  int64_t total_kb = (info.network_bytes + info.cache_bytes) / 1024;
+  int64_t network_kb = info.network_bytes / 1024;
+  int64_t cache_kb = info.cache_bytes / 1024;
+  DCHECK_LE(network_kb, total_kb);
+  DCHECK_LE(cache_kb, total_kb);
+  DCHECK_LE(total_kb, std::numeric_limits<int>::max());
+
+  UMA_HISTOGRAM_CUSTOM_COUNTS(internal::kHistogramNetworkBytesOnComplete,
+                              static_cast<int>(network_kb), 1, 500 * 1024, 50);
+  UMA_HISTOGRAM_CUSTOM_COUNTS(internal::kHistogramCacheBytesOnComplete,
+                              static_cast<int>(cache_kb), 1, 500 * 1024, 50);
+  UMA_HISTOGRAM_CUSTOM_COUNTS(internal::kHistogramTotalBytesOnComplete,
+                              static_cast<int>(total_kb), 1, 500 * 1024, 50);
 }
 
 void CorePageLoadMetricsObserver::OnFailedProvisionalLoad(