Correct or pause previous TimeCounters.

editor/util/plugins/com.google.dart.java2dart/src/com/google/dart/java2dart/engine/MainEngine.java

Index: editor/util/plugins/com.google.dart.java2dart/src/com/google/dart/java2dart/engine/MainEngine.java
diff --git a/editor/util/plugins/com.google.dart.java2dart/src/com/google/dart/java2dart/engine/MainEngine.java b/editor/util/plugins/com.google.dart.java2dart/src/com/google/dart/java2dart/engine/MainEngine.java
index f3ec11f411795caea126e3fe44d675316debdc95..eed6a1fa2adb345887f27bf91e5bd2926e5fde8e 100644
--- a/editor/util/plugins/com.google.dart.java2dart/src/com/google/dart/java2dart/engine/MainEngine.java
+++ b/editor/util/plugins/com.google.dart.java2dart/src/com/google/dart/java2dart/engine/MainEngine.java
@@ -305,31 +305,59 @@ public class MainEngine {
       removeClass(library, "TimeCounter");
       removeClass(library, "TimeCounter_TimeCounterHandle");
       String source = getFormattedSource(library);
-      source += Joiner.on("\n").join(
-          new String[] {
-              "/**",
-              " * Helper for measuring how much time is spent doing some operation.",
-              " */",
-              "class TimeCounter {",
-              "  Stopwatch _sw = new Stopwatch();",
-              "",
-              "  /**",
-              "   * @return the number of milliseconds spent between [start] and [stop].",
-              "   */",
-              "  int get result => _sw.elapsedMilliseconds;",
-              "",
-              "  /**",
-              "   * Starts counting time.",
-              "   *",
-              "   * @return the [TimeCounterHandle] that should be used to stop counting.",
-              "   */",
-              "  TimeCounter_TimeCounterHandle start() => new TimeCounter_TimeCounterHandle(this);",
-              "}", "", "/**",
-              " * The handle object that should be used to stop and update counter.", " */",
-              "class TimeCounter_TimeCounterHandle {", "  final TimeCounter _counter;", "",
-              "  TimeCounter_TimeCounterHandle(this._counter) {", "    _counter._sw.start();",
-              "  }", "", "  /**", "   * Stops counting time and updates counter.", "   */",
-              "  void stop() {", "    _counter._sw.stop();", "  }", "}"});
+      source += makeSource(
+          "/**",
+          " * Helper for measuring how much time is spent doing some operation.",
+          " */",
+          "class TimeCounter {",
+          "  static TimeCounter _current = null;",
+          "  final Stopwatch _sw = new Stopwatch();",
+          "",
+          "  /**",
+          "   * @return the number of milliseconds spent between [start] and [stop].",
+          "   */",
+          "  int get result => _sw.elapsedMilliseconds;",
+          "",
+          "  /**",
+          "   * Starts counting time.",
+          "   *",
+          "   * @return the [TimeCounterHandle] that should be used to stop counting.",
+          "   */",
+          "  TimeCounter_TimeCounterHandle start() {",
+          "    return new TimeCounter_TimeCounterHandle(this);",
+          "  }",
+          "}",
+          "",
+          "/**",
+          " * The handle object that should be used to stop and update counter.",
+          " */",
+          "class TimeCounter_TimeCounterHandle {",
+          "  final TimeCounter _counter;",
+          "  TimeCounter _prev;",
+          "",
+          "  TimeCounter_TimeCounterHandle(this._counter) {",
+          "    // if there is some counter running, pause it",
+          "    _prev = TimeCounter._current;",
+          "    if (_prev != null) {",
+          "      _prev._sw.stop();",
+          "    }",
+          "    TimeCounter._current = _counter;",
+          "    // start this counter",
+          "    _counter._sw.start();",
+          "  }",
+          "",
+          "  /**",
+          "   * Stops counting time and updates counter.",
+          "   */",
+          "  void stop() {",
+          "    _counter._sw.stop();",
+          "    // restore previous counter and resume it",
+          "    TimeCounter._current = _prev;",
+          "    if (_prev != null) {",
+          "      _prev._sw.start();",
+          "    }",
+          "  }",
+          "}");
       Files.write(source, new File(targetFolder + "/utilities_general.dart"), Charsets.UTF_8);
     }
     {