Add UMA for studying download cancellation reasons

content/browser/android/download_controller_android_impl.cc

Index: content/browser/android/download_controller_android_impl.cc
diff --git a/content/browser/android/download_controller_android_impl.cc b/content/browser/android/download_controller_android_impl.cc
index efd07bf2f0e7e52f707a644b97810b510ad761d7..c0180108451d9c1d04f31f314f7833704f7fb0c1 100644
--- a/content/browser/android/download_controller_android_impl.cc
+++ b/content/browser/android/download_controller_android_impl.cc
@@ -13,6 +13,7 @@
 #include "base/bind.h"
 #include "base/lazy_instance.h"
 #include "base/logging.h"
+#include "base/metrics/histogram_macros.h"
 #include "base/synchronization/lock.h"
 #include "base/time/time.h"
 #include "content/browser/android/content_view_core_impl.h"
@@ -131,6 +132,10 @@ static void OnRequestFileAccessResult(JNIEnv* env,
   cb(reinterpret_cast<
       DownloadControllerAndroid::AcquireFileAccessPermissionCallback*>(
       callback_id));
+  if (!granted) {
+    DownloadControllerAndroid::RecordDownloadCancelReason(
+        DownloadControllerAndroid::CANCEL_REASON_NO_STORAGE_PERMISSION);
+  }
   cb->Run(granted);
 }
 
@@ -162,6 +167,13 @@ void DownloadControllerAndroid::SetDownloadControllerAndroid(
 }
 
 // static
+void DownloadControllerAndroid::RecordDownloadCancelReason(
+    DownloadCancelReason reason) {
+  UMA_HISTOGRAM_ENUMERATION(
+      "MobileDownload.CancelReason", reason, CANCEL_REASON_MAX);
+}
+
+// static
 DownloadControllerAndroidImpl* DownloadControllerAndroidImpl::GetInstance() {
   return base::Singleton<DownloadControllerAndroidImpl>::get();
 }
@@ -494,6 +506,8 @@ void DownloadControllerAndroidImpl::OnDownloadUpdated(DownloadItem* item) {
           jmime_type.obj(), jfilename.obj(), jpath.obj(),
           item->GetReceivedBytes(), item->GetId(), jguid.obj(),
           joriginal_url.obj(), jreferrer_url.obj(), item->HasUserGesture());
+      DownloadControllerAndroid::RecordDownloadCancelReason(
+             DownloadControllerAndroid::CANCEL_REASON_NOT_CANCELED);
       break;
     case DownloadItem::CANCELLED:
       Java_DownloadController_onDownloadCancelled(