UMA for data savings displayed to users.

components/data_reduction_proxy/core/browser/data_reduction_proxy_compression_stats.cc

Index: components/data_reduction_proxy/core/browser/data_reduction_proxy_compression_stats.cc
diff --git a/components/data_reduction_proxy/core/browser/data_reduction_proxy_compression_stats.cc b/components/data_reduction_proxy/core/browser/data_reduction_proxy_compression_stats.cc
index 5655e12c92fdd4fc8fe6f62922396b85505649df..6632f84f7749795db795372800db6362360aa238 100644
--- a/components/data_reduction_proxy/core/browser/data_reduction_proxy_compression_stats.cc
+++ b/components/data_reduction_proxy/core/browser/data_reduction_proxy_compression_stats.cc
@@ -704,6 +704,7 @@ void DataReductionProxyCompressionStats::RecordContentLengthPrefs(
     // Here, we prefer collecting less data but the collected data is
     // associated with an accurate date.
     if (days_since_last_update == 1) {
+      RecordUserVisibleDataSavings();
       // The previous day's data point is the second one from the tail.
       // Therefore (kNumDaysInHistory - 2) below.
       RecordDailyContentLengthHistograms(
@@ -721,4 +722,23 @@ void DataReductionProxyCompressionStats::RecordContentLengthPrefs(
   }
 }
 
+void DataReductionProxyCompressionStats::RecordUserVisibleDataSavings() {
+  int64 original_content_length;
+  int64 received_content_length;
+  int64 last_update_internal;
+  GetContentLengths(kNumDaysInHistorySummary, &original_content_length,
+                    &received_content_length, &last_update_internal);
+
+  int64 user_visible_savings_bytes =
+      original_content_length - received_content_length;
+  float user_visible_savings_percent =

[Alexei Svitkine (slow), 2015/06/05 15:46:53]

Nit: No need for float, since the histogram truncated to an int anyway.

[Not at Google. Contact bengr, 2015/06/05 17:59:42]

Done.

+      (float)user_visible_savings_bytes * 100 / original_content_length;

[Alexei Svitkine (slow), 2015/06/05 15:46:53]

Is there any chance that original_content_length would be 0? If so, this would
crash.

[Not at Google. Contact bengr, 2015/06/05 17:59:42]

Good catch. Fixed.

+  UMA_HISTOGRAM_PERCENTAGE(
+      "Net.DailyUserVisibleSavingsPercent_DataRedictionProxyEnabled",
+      user_visible_savings_percent);
+  UMA_HISTOGRAM_COUNTS(
+      "Net.DailyUserVisibleSavingsBytes_DataRedictionProxyEnabled",
+      user_visible_savings_bytes >> 10);
+}
+
 }  // namespace data_reduction_proxy