Add LazyLoad to FP histogram

Change-Id: I03c0eeb61bd02f3c095a72b455de2d7ad3262569
Reviewed-on: https://chromium-review.googlesource.com/1246150Reviewed-by: Ehsan Karamad <ekaramad@chromium.org>
Commit-Queue: Ian Clelland <iclelland@chromium.org>
Cr-Commit-Position: refs/heads/master@{#594390}

tools/metrics/histograms/enums.xml

@@ -20272,6 +20272,7 @@ Called by update_net_error_codes.py.-->
   <int value="26" label="kPictureInPicture"/>
   <int value="27" label="kVerticalScroll"/>
   <int value="28" label="kDocumentWrite"/>
+  <int value="29" label="kLazyLoad"/>
 </enum>
 
 <enum name="FeedbackSource">