[fsp] Move thumbnail logic to Drive specific C++ code.

MetadataCache is soon going to be generalized from Drive to also FSP file
systems. So, in the Files app layer, we should not have Drive specific code.

TEST=Tested manually.
BUG=408017

Review URL: https://codereview.chromium.org/517213002

Cr-Commit-Position: refs/heads/master@{#292829}

chrome/browser/chromeos/extensions/file_manager/private_api_drive.cc

@@ -71,7 +71,10 @@ void FillDriveEntryPropertiesValue(const drive::ResourceEntry& entry_proto,
   const drive::FileSpecificInfo& file_specific_info =
       entry_proto.file_specific_info();
 
-  if (!entry_proto.resource_id().empty()) {
+  // The web thumbnail is used only when the file is not present. Otherwise
+  // it could be out of sync.
+  if (!entry_proto.resource_id().empty() &&
+      !file_specific_info.cache_state().is_present()) {
     properties->thumbnail_url.reset(
         new std::string("https://www.googledrive.com/thumb/" +
                         entry_proto.resource_id() + "?width=500&height=500"));

ui/file_manager/file_manager/foreground/js/thumbnail_loader.js

@@ -49,13 +49,6 @@ function ThumbnailLoader(entry, opt_loaderType, opt_metadata, opt_mediaType,
     };
   }
 
-  // If the file is on the drive and it is present, the file may be out of sync
-  // drive's thumbnail. So we don't use it.
-  if (opt_metadata.drive && opt_metadata.drive.present) {
-    opt_metadata = MetadataCache.cloneMetadata(opt_metadata);
-    opt_metadata.thumbnail = null;
-  }
-
   if (opt_metadata.thumbnail && opt_metadata.thumbnail.url &&
       opt_useEmbedded === ThumbnailLoader.UseEmbedded.USE_EMBEDDED) {
     this.thumbnailUrl_ = opt_metadata.thumbnail.url;