Compile core/mathml/ with -Wshadow.

Bug: 294205
Change-Id: I13561748b18f77d6040bdf1256e3dd003a1b8b4f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2461381Reviewed-by: Rob Buis <rbuis@igalia.com>
Commit-Queue: Morten Stenshorne <mstensho@chromium.org>
Cr-Commit-Position: refs/heads/master@{#815637}

third_party/blink/renderer/core/mathml/BUILD.gn

@@ -5,6 +5,8 @@
 import("//third_party/blink/renderer/core/core.gni")
 
 blink_core_sources("mathml") {
+  configs += [ "//build/config/compiler:noshadowing" ]
+
   sources = [
     "mathml_element.cc",
     "mathml_element.h",

third_party/blink/renderer/core/mathml/mathml_operator_element.cc

@@ -197,7 +197,7 @@ void MathMLOperatorElement::ComputeDictionaryCategory() {
            fallback_form++) {
         if (fallback_form == form)
           continue;
-        auto category = FindCategory(
+        category = FindCategory(
             GetOperatorContent().characters,
             static_cast<MathMLOperatorDictionaryForm>(fallback_form));
         if (category != MathMLOperatorDictionaryCategory::kNone) {