Add some support for the code-point code-unit distinction.

sdk/lib/_internal/compiler/implementation/js_backend/constant_emitter.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 ConstantEmitter implements ConstantVisitor {
   final Compiler compiler;
   final Namer namer;
 
@@ skipping 69 matching lines @@
     buffer.add("true");
   }
 
   void visitFalse(FalseConstant constant) {
     buffer.add("false");
   }
 
   /**
    * Write the contents of the quoted string to a [CodeBuffer] in
    * a form that is valid as JavaScript string literal content.
-   * The string is assumed quoted by single quote characters.
+   * The string is assumed quoted by double quote characters.
    */
-  void writeEscapedString(DartString string,
-                          CodeBuffer buffer,
-                          Node diagnosticNode) {
-    void onError(code) {
-      compiler.reportError(
-          diagnosticNode,
-          'Unhandled non-BMP character: U+${code.toRadixString(16)}');
-    }
-    writeJsonEscapedCharsOn(string.iterator(), buffer, onError);
-  }
-
   void visitString(StringConstant constant) {
-    buffer.add("'");
-    writeEscapedString(constant.value, buffer, constant.node);
-    buffer.add("'");
+    buffer.add('"');
+    writeJsonEscapedCharsOn(constant.value.slowToString(), buffer);
+    buffer.add('"');
   }
 
   void emitCanonicalVersion(Constant constant) {
     String name = namer.constantName(constant);
     buffer.add(namer.isolatePropertiesAccessForConstant(name));
   }
 
   void visitList(ListConstant constant) {
     if (shouldEmitCanonicalVersion) {
       emitCanonicalVersion(constant);
@@ skipping 89 matching lines @@
       buffer.add(getJsConstructor(constant.type.element));
       buffer.add("(");
       for (int i = 0; i < constant.fields.length; i++) {
         if (i != 0) buffer.add(", ");
         _visit(constant.fields[i]);
       }
       buffer.add(")");
     }
   }
 }