Download: Sync prompt for android preference.

This preference controls whether to popup download location dialog,
should be synced.

Bug: 1024400
Change-Id: Ic31c7a338ecded3833022badf7ffb8e03ab7e453
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1918659Reviewed-by: David Trainor <dtrainor@chromium.org>
Commit-Queue: Xing Liu <xingliu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#715936}

chrome/browser/download/download_prefs.cc

@@ -269,8 +269,10 @@ void DownloadPrefs::RegisterProfilePrefs(
       base::FeatureList::IsEnabled(features::kDownloadsLocationChange)
           ? DownloadPromptStatus::SHOW_INITIAL
           : DownloadPromptStatus::DONT_SHOW;
-  registry->RegisterIntegerPref(prefs::kPromptForDownloadAndroid,
-                                static_cast<int>(download_prompt_status));
+  registry->RegisterIntegerPref(
+      prefs::kPromptForDownloadAndroid,
+      static_cast<int>(download_prompt_status),
+      user_prefs::PrefRegistrySyncable::SYNCABLE_PREF);
   registry->RegisterBooleanPref(
       prefs::kShowMissingSdCardErrorAndroid,
       base::FeatureList::IsEnabled(features::kDownloadsLocationChange));