Enabling sampling of UMA and crash reports on Android.

chrome/android/java/src/org/chromium/chrome/browser/metrics/UmaSessionStats.java

Index: chrome/android/java/src/org/chromium/chrome/browser/metrics/UmaSessionStats.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/metrics/UmaSessionStats.java b/chrome/android/java/src/org/chromium/chrome/browser/metrics/UmaSessionStats.java
index 2ebed96d34158787b336c2510d21812985576498..fb98c91138a7c7cab6ab93295ef88e714420b4c1 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/metrics/UmaSessionStats.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/metrics/UmaSessionStats.java
@@ -153,7 +153,9 @@ public class UmaSessionStats implements NetworkChangeNotifier.ConnectionTypeObse
     }
 
     /**
-     * Updates the state of the MetricsService to account for the user's preferences.
+     * Updates the state of the MetricsService to account for the user's preferences. Android prefs
+     * and Chrome Local State prefs for metrics reporting should be in sync before calling this
+     * function.
      */
     public void updateMetricsServiceState() {
         boolean mayRecordStats = !PrivacyPreferencesManager.getInstance()
@@ -192,6 +194,9 @@ public class UmaSessionStats implements NetworkChangeNotifier.ConnectionTypeObse
             prefManager.setUsageAndCrashReporting(prefBridge.isMetricsReportingEnabled());
         }
 
+        // Update the metrics sampling state.

[Alexei Svitkine (slow), 2016/08/18 06:16:39]

Expand comment to mention why this is being done - i.e. "so that it can be used
by Java code before native is initialized.".

[jwd, 2016/08/23 18:40:03]

Done.

+        prefManager.setClientInMetricsSample(UmaUtils.isClientInSample());
+
         // Make sure preferences are in sync.
         prefManager.syncUsageAndCrashReportingPrefs();
     }