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

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

Index: sdk/lib/_internal/compiler/implementation/js_backend/constant_emitter.dart
diff --git a/sdk/lib/_internal/compiler/implementation/js_backend/constant_emitter.dart b/sdk/lib/_internal/compiler/implementation/js_backend/constant_emitter.dart
index 7738b57af2214acc80e440d8042b4735705fc2b0..a9e49c0f3a94f4bd2e4135cc72eef5626c55527f 100644
--- a/sdk/lib/_internal/compiler/implementation/js_backend/constant_emitter.dart
+++ b/sdk/lib/_internal/compiler/implementation/js_backend/constant_emitter.dart
@@ -87,12 +87,23 @@ class ConstantEmitter implements ConstantVisitor {
   /**
    * 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 double quote characters.
+   * The string is assumed quoted by single 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('"');
-    writeJsonEscapedCharsOn(constant.value.slowToString(), buffer);
-    buffer.add('"');
+    buffer.add("'");
+    writeEscapedString(constant.value, buffer, constant.node);
+    buffer.add("'");
   }
 
   void emitCanonicalVersion(Constant constant) {