[regexp] Mark functions MUST_USE_RESULT

BUG=v8:5339

Review-Url: https://codereview.chromium.org/2442333002
Cr-Commit-Position: refs/heads/master@{#40545}

src/builtins/builtins-regexp.cc

@@ -39,10 +39,10 @@ Handle<String> PatternFlags(Isolate* isolate, Handle<JSRegExp> regexp) {
 
 // ES#sec-regexpinitialize
 // Runtime Semantics: RegExpInitialize ( obj, pattern, flags )
-MaybeHandle<JSRegExp> RegExpInitialize(Isolate* isolate,
-                                       Handle<JSRegExp> regexp,
-                                       Handle<Object> pattern,
-                                       Handle<Object> flags) {
+MUST_USE_RESULT MaybeHandle<JSRegExp> RegExpInitialize(Isolate* isolate,
+                                                       Handle<JSRegExp> regexp,
+                                                       Handle<Object> pattern,
+                                                       Handle<Object> flags) {
   Handle<String> pattern_string;
   if (pattern->IsUndefined(isolate)) {
     pattern_string = isolate->factory()->empty_string();
@@ -1341,9 +1341,9 @@ MaybeHandle<JSArray> RegExpSplit(Isolate* isolate, Handle<JSRegExp> regexp,
 
 // ES##sec-speciesconstructor
 // SpeciesConstructor ( O, defaultConstructor )
-MaybeHandle<Object> SpeciesConstructor(Isolate* isolate,
-                                       Handle<JSReceiver> recv,
-                                       Handle<JSFunction> default_ctor) {
+MUST_USE_RESULT MaybeHandle<Object> SpeciesConstructor(
+    Isolate* isolate, Handle<JSReceiver> recv,
+    Handle<JSFunction> default_ctor) {
   Handle<Object> ctor_obj;
   ASSIGN_RETURN_ON_EXCEPTION(
       isolate, ctor_obj,

src/regexp/regexp-utils.h

@@ -19,16 +19,15 @@ class RegExpUtils : public AllStatic {
                                              int capture, bool* ok = nullptr);
 
   // Last index (RegExp.lastIndex) accessors.
-  static MaybeHandle<Object> SetLastIndex(Isolate* isolate,
-                                          Handle<JSReceiver> regexp, int value);
-  static MaybeHandle<Object> GetLastIndex(Isolate* isolate,
-                                          Handle<JSReceiver> recv);
+  static MUST_USE_RESULT MaybeHandle<Object> SetLastIndex(
+      Isolate* isolate, Handle<JSReceiver> regexp, int value);
+  static MUST_USE_RESULT MaybeHandle<Object> GetLastIndex(
+      Isolate* isolate, Handle<JSReceiver> recv);
 
   // ES#sec-regexpexec Runtime Semantics: RegExpExec ( R, S )
-  static MaybeHandle<Object> RegExpExec(Isolate* isolate,
-                                        Handle<JSReceiver> regexp,
-                                        Handle<String> string,
-                                        Handle<Object> exec);
+  static MUST_USE_RESULT MaybeHandle<Object> RegExpExec(
+      Isolate* isolate, Handle<JSReceiver> regexp, Handle<String> string,
+      Handle<Object> exec);
 
   // ES#sec-isregexp IsRegExp ( argument )
   // Includes checking of the match property.
@@ -42,10 +41,9 @@ class RegExpUtils : public AllStatic {
   // AdvanceStringIndex ( S, index, unicode )
   static int AdvanceStringIndex(Isolate* isolate, Handle<String> string,
                                 int index, bool unicode);
-  static MaybeHandle<Object> SetAdvancedStringIndex(Isolate* isolate,
-                                                    Handle<JSReceiver> regexp,
-                                                    Handle<String> string,
-                                                    bool unicode);
+  static MUST_USE_RESULT MaybeHandle<Object> SetAdvancedStringIndex(
+      Isolate* isolate, Handle<JSReceiver> regexp, Handle<String> string,
+      bool unicode);
 };
 
 }  // namespace internal

src/runtime/runtime-regexp.cc

@@ -1124,7 +1124,7 @@ static Object* SearchRegExpMultiple(Isolate* isolate, Handle<String> subject,
   }
 }
 
-MaybeHandle<String> StringReplaceNonGlobalRegExpWithFunction(
+MUST_USE_RESULT MaybeHandle<String> StringReplaceNonGlobalRegExpWithFunction(
     Isolate* isolate, Handle<String> subject, Handle<JSRegExp> regexp,
     Handle<Object> replace_obj) {
   Factory* factory = isolate->factory();
@@ -1193,9 +1193,10 @@ MaybeHandle<String> StringReplaceNonGlobalRegExpWithFunction(
 
 // Legacy implementation of RegExp.prototype[Symbol.replace] which
 // doesn't properly call the underlying exec method.
-MaybeHandle<String> RegExpReplace(Isolate* isolate, Handle<JSRegExp> regexp,
-                                  Handle<String> string,
-                                  Handle<Object> replace_obj) {
+MUST_USE_RESULT MaybeHandle<String> RegExpReplace(Isolate* isolate,
+                                                  Handle<JSRegExp> regexp,
+                                                  Handle<String> string,
+                                                  Handle<Object> replace_obj) {
   Factory* factory = isolate->factory();
 
   // TODO(jgruber): We need the even stricter guarantee of an unmodified