Fix path passing for pre-commit.

Also fix filename separators on Windows.

b/150775273

.pre-commit-config.yaml

@@ -206,9 +206,9 @@ repos:
         files: '.*\.gni?$'
     -   id: meta-validate
         name: Validate METADATA files
-        entry: python tools/metadata/validate.py
+        entry: python -m tools.metadata.validate
         language: python
         additional_dependencies:
           - "protobuf"
         always_run: true
-        pass_filenames: true
+        pass_filenames: false

base/METADATA

@@ -18,3 +18,4 @@ third_party {
     day: 23
   }
 }
+break this this too

tools/metadata/validate.py

@@ -70,11 +70,11 @@ def update_proto():
 
 
 def filter_files(path):
-  if not path.endswith('/METADATA'):
+  if not path.endswith(os.path.sep + 'METADATA'):
     return False
-  if '.dist-info/' in path:
+  if '.dist-info' in path:
     return False  # Python packaging files
-  if 'skia/site' in path:
+  if os.path.join('skia', 'site') in path:
     return False  # Different upstream files
   return True