Use the currently-mounted Drive path in the drive-internals webui.

Currently drive-internals displays a path specific to the current
implementation as the Drive mount path. When running with DriveFS
enabled, this path is incorrect.

Obtain the path from DriveIntegrationService instead so the correct path
is displayed.

Bug: 829703
Change-Id: Ie0f3a36c742c9476ce18c0cbede83d15ab670c53
Reviewed-on: https://chromium-review.googlesource.com/1182901
Commit-Queue: Sam McNally <sammc@chromium.org>
Reviewed-by: Noel Gordon <noel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#584670}

chrome/browser/ui/webui/chromeos/drive_internals_ui.cc

@@ -787,9 +787,11 @@ void DriveInternalsWebUIHandler::UpdatePathConfigurationsSection() {
   AppendKeyValue(
       &paths, "Downloads",
       file_manager::util::GetDownloadsFolderForProfile(profile).AsUTF8Unsafe());
-  AppendKeyValue(
-      &paths, "Drive",
-      drive::util::GetDriveMountPointPath(profile).AsUTF8Unsafe());
+  const auto* integration_service = GetIntegrationService();
+  if (integration_service && integration_service->IsMounted()) {
+    AppendKeyValue(&paths, "Drive",
+                   integration_service->GetMountPointPath().AsUTF8Unsafe());
+  }
 
   const char* kPathPreferences[] = {
     prefs::kSelectFileLastDirectory,