Preserve the contents of Dart strings with unmatched surrogate halfs by avoiding a UTF16 -> UTF8

runtime/bin/vmservice/observatory/tests/ui/inspector.dart

 // Copyright (c) 2014, 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.
 
 // See inspector.txt for expected behavior.
 
 library manual_inspector_test;
 
 import 'dart:isolate';
 import 'dart:mirrors';
@@ skipping 28 matching lines @@
 var mirrorReference;
 var portReceive;
 var portSend;
 var regex;
 var smi;
 var stacktrace;
 var string;
 var stringEscapedUnicodeEscape;
 var stringHebrew;
 var stringLatin1;
+var stringMalformedLead;
+var stringMalformedTrail;
 var stringNewLinesAndTabs;
 var stringNullInTheMiddle;
 var stringSnowflake;
 var stringTrebleClefs;
 var stringUnicode;
 var theFalse;
 var theNull;
 var theTrue;
 var type;
 var typeParameter;
@@ skipping 69 matching lines @@
   mirrorInstance = reflect("a reflectee");
   mirrorReference = extractPrivateField(mirrorClass, '_reflectee');
   portReceive = new RawReceivePort();
   regex = new RegExp("a*b+c");
   smi = 7;
   stacktrace = genStacktrace();
   string = "Hello";
   stringEscapedUnicodeEscape = "Should not be A: \\u0041";
   stringHebrew = "שלום רב שובך צפורה נחמדת";  // Right-to-left text.
   stringLatin1 = "blåbærgrød";
+  stringMalformedLead = "before" + "𝄞"[0] + "after";
+  stringMalformedTrail = "before" + "𝄞"[1] + "after";
   stringNewLinesAndTabs = "One fish\ttwo fish\nRed fish\tBlue fish\n";
   stringNullInTheMiddle = "There are four\u0000 words.";
   stringSnowflake = "❄";
   stringTrebleClefs = "1𝄞2𝄞𝄞3𝄞𝄞𝄞";  // Surrogate pair.
   stringUnicode = "Îñţérñåţîöñåļîžåţîờñ";
   theFalse = false;
   theNull = null;
   theTrue = true;
   type = String;
   typeParameter = extractPrivateField(reflectClass(A).typeVariables.single, '_reflectee');
   typedData = extractPrivateField(new ByteData(64), '_typedData');
   userTag = new UserTag("Example tag name");
   weakProperty = extractPrivateField(expando, '_data').firstWhere((e) => e != null);
 
   Isolate.spawn(secondMain, "Hello").then((otherIsolate) {
     isolate = otherIsolate;
     portSend = otherIsolate.controlPort;
     capability = otherIsolate.terminateCapability;
   });
 
   print("Finished main");
 }