NTP: Fix TileType metrics on desktop

chrome/browser/resources/local_ntp/most_visited_single.js

Index: chrome/browser/resources/local_ntp/most_visited_single.js
diff --git a/chrome/browser/resources/local_ntp/most_visited_single.js b/chrome/browser/resources/local_ntp/most_visited_single.js
index 5529abf88ea7375267be4b3815f52a2810586ab2..9eb0b16a6e9db07d1baca84f58798a5293b01781 100644
--- a/chrome/browser/resources/local_ntp/most_visited_single.js
+++ b/chrome/browser/resources/local_ntp/most_visited_single.js
@@ -51,8 +51,8 @@ var TileVisualType = {
   ICON_REAL: 1,
   ICON_COLOR: 2,
   ICON_DEFAULT: 3,
-  THUMBNAIL: 4,
-  THUMBNAIL_FAILED: 5,
+  THUMBNAIL: 7,
+  THUMBNAIL_FAILED: 8,

[Ilya Sherman, 2017/04/21 19:58:38]

I'm confused about why there is a gap in this enum.  It sounds like there's a
Java-side enum as well, and the two need to be kept in sync?  That sounds really
fragile.  If my understanding is correct, please move all of the enumerated
constants into C++, and expose them to Java.  (I know that I've seen this done
elsewhere in the codebase, though I don't have a reference handy,
unfortunately.)

Also, if my understanding is correct, then the histograms recording these
metrics are going to have conflated data for some buckets.  The best practice in
this case is to rename the histograms, so that the active histograms have
internally consistent semantics.

 };