Temporary disable validate_prefix.py

Temporary disable validate_prefix.py until we split all histograms
because this blocks all updates in the current histograms.xml.

Bug: 1120228
Change-Id: I5f3a607942098c4aa9341d1f86dda7913d185c49
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2368080
Auto-Submit: Weilun Shi <sweilun@chromium.org>
Commit-Queue: Alexei Svitkine <asvitkine@chromium.org>
Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
Cr-Commit-Position: refs/heads/master@{#800550}

tools/metrics/histograms/PRESUBMIT.py

@@ -86,7 +86,9 @@ def ValidateSingleFile(input_api, output_api, file_obj, cwd, results):
   # If the changed file is histograms.xml, pretty-print and validate prefix it.
   elif 'histograms.xml' in filepath:
     GetPrettyPrintErrors(input_api, output_api, cwd, filepath, results)
-    GetPrefixErrors(input_api, output_api, cwd, filepath, results)
+    # TODO(crbug/1120229): Re-enable validate prefix check once all histograms
+    # are split.
+    # GetPrefixErrors(input_api, output_api, cwd, filepath, results)
     return True
 
   # If the changed file is enums.xml, pretty-print it.