Add use counters for IsRegExp

A spec change to simplify IsRegExp has been proposed:

https://github.com/tc39/ecma262/pull/1318

This CL adds use counters for cases in which the spec change would
alter behavior:

1. o[@@match] is trueish but o is not a JSRegExp
2. o[@@match] is falseish (but not undefined) and o is a JSRegExp

This is the Chromium side of required changes.
The V8-side CL: https://crrev.com/c/1360630

Bug: v8:8522
Change-Id: I2ec9b1a5f54f8e70a02e48f280a548871990aabd
Reviewed-on: https://chromium-review.googlesource.com/c/1360730Reviewed-by: Nico Weber <thakis@chromium.org>
Reviewed-by: Marja Hölttä <marja@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#615507}

third_party/blink/public/platform/web_feature.mojom

@@ -2088,6 +2088,8 @@ enum WebFeature {
   kCSSSelectorNotWithPartiallyValidList = 2647,
   kV8IDBFactory_Databases_Method = 2648,
   kOpenerNavigationDownloadCrossOriginNoGesture = 2649,
+  kV8RegExpMatchIsTrueishOnNonJSRegExp = 2650,
+  kV8RegExpMatchIsFalseishOnJSRegExp = 2651,
 
   // Add new features immediately above this line. Don't change assigned
   // numbers of any item, and don't reuse removed slots.

third_party/blink/renderer/bindings/core/v8/use_counter_callback.cc

@@ -217,6 +217,12 @@ void UseCounterCallback(v8::Isolate* isolate,
     case v8::Isolate::kOptimizedFunctionWithOneShotBytecode:
       blink_feature = WebFeature::kV8OptimizedFunctionWithOneShotBytecode;
       break;
+    case v8::Isolate::kRegExpMatchIsTrueishOnNonJSRegExp:
+      blink_feature = WebFeature::kV8RegExpMatchIsTrueishOnNonJSRegExp;
+      break;
+    case v8::Isolate::kRegExpMatchIsFalseishOnJSRegExp:
+      blink_feature = WebFeature::kV8RegExpMatchIsFalseishOnJSRegExp;
+      break;
     default:
       // This can happen if V8 has added counters that this version of Blink
       // does not know about. It's harmless.

tools/metrics/histograms/enums.xml

@@ -20997,6 +20997,8 @@ Called by update_net_error_codes.py.-->
   <int value="2647" label="CSSSelectorNotWithPartiallyValidList"/>
   <int value="2648" label="V8IDBFactory_Databases_Method"/>
   <int value="2649" label="OpenerNavigationDownloadCrossOriginNoGesture"/>
+  <int value="2650" label="V8RegExpMatchIsTrueishOnNonJSRegExp"/>
+  <int value="2651" label="V8RegExpMatchIsFalseishOnJSRegExp"/>
 </enum>
 
 <enum name="FeaturePolicyFeature">