Add AddEntriesMessage::ConvertJSONValue helper

Add a AddEntriesMessage helper to convert the JSON dictionary value of
the addEntries command to an AddEntriesMessage |message|.

In the addEntries command, use that converter to extract the |message|
and also FAIL if the message.volume is an invalid volume type.

Covered by existing FileManager browser tests.

Bug: 833834
Change-Id: Ib7ec56fee7c5b4857ccdfb0155a414430db73e97
Reviewed-on: https://chromium-review.googlesource.com/1042125Reviewed-by: Noel Gordon <noel@chromium.org>
Reviewed-by: Stuart Langley <slangley@chromium.org>
Commit-Queue: Noel Gordon <noel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#555922}

chrome/browser/chromeos/file_manager/file_manager_browsertest_base.cc

@@ -138,7 +138,14 @@ struct AddEntriesMessage {
   // Target volume to add |entries| to.
   TargetVolume volume;
 
-  // Registers the member information to the given converter.
+  // Converts |value| to an AddEntriesMessage: true on success.
+  static bool ConvertJSONValue(const base::DictionaryValue& value,
+                               AddEntriesMessage* message) {
+    base::JSONValueConverter<AddEntriesMessage> converter;
+    return converter.Convert(value, message);
+  }
+
+  // Registers AddEntriesMessage member info to the |converter|.
   static void RegisterJSONConverter(
       base::JSONValueConverter<AddEntriesMessage>* converter) {
     converter->RegisterCustomField("volume", &AddEntriesMessage::volume,
@@ -707,10 +714,9 @@ void FileManagerBrowserTestBase::OnCommand(const std::string& name,
   }
 
   if (name == "addEntries") {
-    // Add entries to the specified volume.
-    base::JSONValueConverter<AddEntriesMessage> add_entries_message_converter;
+    // Add the message.entries to the message.volume.
     AddEntriesMessage message;
-    ASSERT_TRUE(add_entries_message_converter.Convert(value, &message));
+    ASSERT_TRUE(AddEntriesMessage::ConvertJSONValue(value, &message));
 
     for (size_t i = 0; i < message.entries.size(); ++i) {
       switch (message.volume) {
@@ -725,9 +731,6 @@ void FileManagerBrowserTestBase::OnCommand(const std::string& name,
           if (usb_volume_)
             usb_volume_->CreateEntry(*message.entries[i]);
           break;
-        default:
-          NOTREACHED();
-          break;
       }
     }