metrics_xml_format: check the XML path against realpath

metrics_xml_format checks the given file path to ensure that
it's an XML under tools/metrics with the following steps.
1. convert the input file path as a real path.
2. check the real path starts with
  GetPrimarySolutionPath() + "/tools/metrics"

This doesn't work as intended if GetPrimarySolutionPath() returns
a symblink.

This patch converts GetPrimarySolutionPath() as a realpath to ensure
it runs the check based on the realpath of the git checkout.

Bug: 396182402
Change-Id: I3207eba7ed52d09a01b38d65fcf7c314622d95cb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/6279842
Auto-Submit: Scott Lee <ddoman@chromium.org>
Commit-Queue: Gavin Mak <gavinmak@google.com>
Reviewed-by: Gavin Mak <gavinmak@google.com>

metrics_xml_format.py

@@ -12,6 +12,7 @@ import sys
 
 
 def GetMetricsDir(top_dir, path):
+    top_dir = os.path.realpath(top_dir)
     metrics_xml_dirs = [
         os.path.join(top_dir, 'tools', 'metrics', 'actions'),
         os.path.join(top_dir, 'tools', 'metrics', 'histograms'),
@@ -45,10 +46,12 @@ def FindMetricsXMLFormatterTool(path, verbose=False):
     if not top_dir:
         log('Not executed in a Chromium checkout; skip formatting', verbose)
         return ''
+
     xml_dir = GetMetricsDir(top_dir, path)
     if not xml_dir:
         log(f'{path} is not a metric XML; skip formatting', verbose)
         return ''
+
     # Just to ensure that the given file is located in the current checkout
     # folder. If not, skip the formatting.
     if not os.path.realpath(path).startswith(os.path.realpath(top_dir)):