Turn a Dart String + String into a JavaScript String + String.

sdk/lib/_internal/compiler/implementation/js_backend/backend.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of js_backend;
 
 class JavaScriptItemCompilationContext extends ItemCompilationContext {
   final Set<HInstruction> boundsChecked;
 
   JavaScriptItemCompilationContext()
@@ skipping 172 matching lines @@
   ClassElement jsMutableIndexableClass;
 
   ClassElement jsMutableArrayClass;
   ClassElement jsFixedArrayClass;
   ClassElement jsExtendableArrayClass;
 
   Element jsIndexableLength;
   Element jsArrayRemoveLast;
   Element jsArrayAdd;
   Element jsStringSplit;
-  Element jsStringConcat;
   Element jsStringToString;
+  Element jsStringOperatorAdd;
   Element objectEquals;
 
   ClassElement typeLiteralClass;
   ClassElement mapLiteralClass;
   ClassElement constMapLiteralClass;
 
   Element getInterceptorMethod;
   Element interceptedNames;
 
   /**
@@ skipping 402 matching lines @@
 
     jsArrayClass.ensureResolved(compiler);
     jsArrayRemoveLast = compiler.lookupElementIn(
         jsArrayClass, const SourceString('removeLast'));
     jsArrayAdd = compiler.lookupElementIn(
         jsArrayClass, const SourceString('add'));
 
     jsStringClass.ensureResolved(compiler);
     jsStringSplit = compiler.lookupElementIn(
         jsStringClass, const SourceString('split'));
-    jsStringConcat = compiler.lookupElementIn(
-        jsStringClass, const SourceString('concat'));
+    jsStringOperatorAdd = compiler.lookupElementIn(
+        jsStringClass, const SourceString('+'));
     jsStringToString = compiler.lookupElementIn(
         jsStringClass, const SourceString('toString'));
 
     typeLiteralClass = compiler.findHelper(const SourceString('TypeImpl'));
     mapLiteralClass =
         compiler.coreLibrary.find(const SourceString('LinkedHashMap'));
     constMapLiteralClass =
         compiler.findHelper(const SourceString('ConstantMap'));
 
     objectEquals = compiler.lookupElementIn(
@@ skipping 1150 matching lines @@
     copy(constant.values);
     copy(constant.protoValue);
     copy(constant);
   }
 
   void visitConstructed(ConstructedConstant constant) {
     copy(constant.fields);
     copy(constant);
   }
 }