Don't double-escape in strings in the VM Service, and don't use \u0000 to determine the string lengt

runtime/bin/vmservice/observatory/test/string_escaping_test.dart

Index: runtime/bin/vmservice/observatory/test/string_escaping_test.dart
diff --git a/runtime/bin/vmservice/observatory/test/string_escaping_test.dart b/runtime/bin/vmservice/observatory/test/string_escaping_test.dart
new file mode 100644
index 0000000000000000000000000000000000000000..cf581b7d101cab2ed24b4a930ac38369aea4f462
--- /dev/null
+++ b/runtime/bin/vmservice/observatory/test/string_escaping_test.dart
@@ -0,0 +1,81 @@
+// 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.
+
+library string_escaping_test;
+
+import 'dart:async';
+import 'dart:mirrors';
+import 'package:observatory/service_io.dart';
+import 'package:unittest/unittest.dart';
+import 'test_helper.dart';
+
+var ascii;
+var latin1;
+var unicode;
+var hebrew;
+var singleQuotes;
+var doubleQuotes;
+var newLines;
+var tabs;
+var suggrogatePairs;
+var nullInTheMiddle;
+var escapedUnicodeEscape;
+var longStringEven;
+var longStringOdd;
+
+void script() {
+  ascii = "Hello, World!";
+  latin1 = "blåbærgrød";
+  unicode = "Îñţérñåţîöñåļîžåţîờñ";
+  hebrew = "שלום רב שובך צפורה נחמדת";  // Right-to-left text.
+  singleQuotes = "'One,' he said.";
+  doubleQuotes = '"Two," he said.';
+  newLines = "Windows\r\nSmalltalk\rUnix\n";
+  tabs = "One\tTwo\tThree";
+  suggrogatePairs = "1𝄞2𝄞𝄞3𝄞𝄞𝄞";
+  nullInTheMiddle = "There are four\u0000 words.";
+  escapedUnicodeEscape = "Should not be A: \\u0041";
+
+  // A surrogate pair will cross the preferred truncation boundry.
+  longStringEven = "..";
+  for (int i = 0; i < 512; i++) longStringEven += "𝄞";
+  longStringOdd = ".";
+  for (int i = 0; i < 512; i++) longStringOdd += "𝄞";
+}
+
+var tests = [
+
+(Isolate isolate) =>
+  isolate.rootLib.load().then((Library lib) {
+    expectFullString(String varName, String varValueAsString) {
+      ServiceMap field = lib.variables.singleWhere((v) => v.name == varName);
+      Instance value = field['value'];
+      expect(value.valueAsString, equals(varValueAsString));
+      expect(value.valueAsStringIsTruncated, isFalse);
+    }
+    expectTruncatedString(String varName, String varValueAsString) {
+      ServiceMap field = lib.variables.singleWhere((v) => v.name == varName);
+      Instance value = field['value'];
+      expect(varValueAsString, startsWith(value.valueAsString));
+      expect(value.valueAsStringIsTruncated, isTrue);
+    }
+
+    script();  // Need to initialize variables in the testing isolate.
+    expectFullString('ascii', ascii);
+    expectFullString('latin1', latin1);
+    expectFullString('unicode', unicode);
+    expectFullString('hebrew', hebrew);
+    expectFullString('singleQuotes', singleQuotes);
+    expectFullString('doubleQuotes', doubleQuotes);
+    expectFullString('newLines', newLines);
+    expectFullString('tabs', tabs);
+    expectFullString('suggrogatePairs', suggrogatePairs);
+    expectFullString('nullInTheMiddle', nullInTheMiddle);  /// 01: ok
+    expectTruncatedString('longStringEven', longStringEven);
+    expectTruncatedString('longStringOdd', longStringOdd);
+  }),
+
+];
+
+main(args) => runIsolateTests(args, tests, testeeBefore: script);