Typecheck chrome://downloads using CompilerPass.java

chrome/browser/ui/webui/downloads_dom_handler.cc

Index: chrome/browser/ui/webui/downloads_dom_handler.cc
diff --git a/chrome/browser/ui/webui/downloads_dom_handler.cc b/chrome/browser/ui/webui/downloads_dom_handler.cc
index 84ec86f96d6877e8b02fa0357c91f7822b14a9b2..e917015ce9adb26da7d1764f1bb186186ed9e627 100644
--- a/chrome/browser/ui/webui/downloads_dom_handler.cc
+++ b/chrome/browser/ui/webui/downloads_dom_handler.cc
@@ -118,6 +118,11 @@ base::DictionaryValue* CreateDownloadItemValue(
   // progress. The difference currently only matters to Drive downloads and
   // those don't show up on the downloads page, but should.
   DownloadItemModel download_model(download_item);
+
+  // The items which are to be written into file_value are also described in
+  // chrome/browser/resources/downloads/downloads.js in @typedef for
+  // BackendDownloadObject. Please update it whenever you add or remove
+  // any keys in file_value.
   base::DictionaryValue* file_value = new base::DictionaryValue();
 
   file_value->SetInteger(