Presubmit check forbidding tab characters in source files.

WebKit's Subversion repository forbids tab characters in source files.
Follow-up to:
https://chromium-review.googlesource.com/c/angle/angle/+/1954410

Bug: angleproject:3439
Change-Id: I7ab170cae6985c62ee2f163c15d2746f620fe648
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1959750
Commit-Queue: James Darpinian <jdarpinian@chromium.org>
Reviewed-by: Jonah Ryan-Davis <jonahr@google.com>

PRESUBMIT.py

@@ -13,8 +13,8 @@ import subprocess
 import sys
 import tempfile
 
-# Fragment of a regular expression that matches C++ and Objective-C++ implementation files.
-_IMPLEMENTATION_EXTENSIONS = r'\.(cc|cpp|cxx|mm)$'
+# Fragment of a regular expression that matches C++ and Objective-C++ implementation files and headers.
+_IMPLEMENTATION_AND_HEADER_EXTENSIONS = r'\.(cc|cpp|cxx|mm|h|hpp|hxx)$'
 
 # Fragment of a regular expression that matches C++ and Objective-C++ header files.
 _HEADER_EXTENSIONS = r'\.(h|hpp|hxx)$'
@@ -147,8 +147,36 @@ def _CheckExportValidity(input_api, output_api):
         shutil.rmtree(outdir)
 
 
+def _CheckTabsInSourceFiles(input_api, output_api):
+    """Forbids tab characters in source files due to a WebKit repo requirement. """
+
+    def implementation_and_headers(f):
+        return input_api.FilterSourceFile(
+            f, white_list=(r'.+%s' % _IMPLEMENTATION_AND_HEADER_EXTENSIONS,))
+
+    files_with_tabs = []
+    for f in input_api.AffectedSourceFiles(implementation_and_headers):
+        for (num, line) in f.ChangedContents():
+            if '\t' in line:
+                files_with_tabs.append(f)
+                break
+
+    if files_with_tabs:
+        return [
+            output_api.PresubmitError(
+                'Tab characters in source files.',
+                items=sorted(files_with_tabs),
+                long_text=
+                'Tab characters are forbidden in ANGLE source files because WebKit\'s Subversion\n'
+                'repository does not allow tab characters in source files.\n'
+                'Please remove tab characters from these files.')
+        ]
+    return []
+
+
 def CheckChangeOnUpload(input_api, output_api):
     results = []
+    results.extend(_CheckTabsInSourceFiles(input_api, output_api))
     results.extend(_CheckCodeGeneration(input_api, output_api))
     results.extend(_CheckChangeHasBugField(input_api, output_api))
     results.extend(input_api.canned_checks.CheckChangeHasDescription(input_api, output_api))