[WebLayer] Add missing impl->public type conversion for NewTabType

implTypeToJavaType was never getting called on the int that got passed
back to the client.

Change-Id: I3ae969989d5c2b6fec5842e0cf026ee296a24337
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2276764
Auto-Submit: Clark DuVall <cduvall@chromium.org>
Commit-Queue: John Abd-El-Malek <jam@chromium.org>
Reviewed-by: John Abd-El-Malek <jam@chromium.org>
Cr-Commit-Position: refs/heads/master@{#784464}

weblayer/browser/java/org/chromium/weblayer_private/NewTabCallbackProxy.java

@@ -52,7 +52,7 @@ public final class NewTabCallbackProxy {
         // This class should only be created while the tab is attached to a fragment.
         assert mTab.getBrowser() != null;
         assert mTab.getBrowser().equals(tab.getBrowser());
-        mTab.getClient().onNewTab(tab.getId(), mode);
+        mTab.getClient().onNewTab(tab.getId(), implTypeToJavaType(mode));
     }
 
     @CalledByNative