Add UMA metric to track the time elapsed since a WebAPK was last launched

base/android/record_histogram.cc

Index: base/android/record_histogram.cc
diff --git a/base/android/record_histogram.cc b/base/android/record_histogram.cc
index 1a207a18dc42b5d7fb91dd4cff45130017bc6c4c..aa2d2a56f7ddd41cc7cf095937a805a8a9403dca 100644
--- a/base/android/record_histogram.cc
+++ b/base/android/record_histogram.cc
@@ -315,6 +315,21 @@ jint GetHistogramValueCountForTesting(
   return samples->GetCount(static_cast<int>(sample));
 }
 
+jint GetHistogramTotalCountForTesting(
+    JNIEnv* env,
+    const JavaParamRef<jclass>& clazz,
+    const JavaParamRef<jstring>& histogram_name) {
+  HistogramBase* histogram = StatisticsRecorder::FindHistogram(
+      android::ConvertJavaStringToUTF8(env, histogram_name));
+  if (histogram == nullptr) {
+    // No samples have been recorded for this histogram.
+    return 0;
+  }
+
+  std::unique_ptr<HistogramSamples> samples = histogram->SnapshotSamples();
+  return samples->TotalCount();

[Xi Han, 2017/06/14 14:51:06]

Please remove |samples| and return histogram->SnapshotSamples()->TotalCount().

+}
+
 bool RegisterRecordHistogram(JNIEnv* env) {
   return RegisterNativesImpl(env);
 }