dart2js: Measure time of individual optimization passes.

pkg/compiler/lib/src/common/tasks.dart

Index: pkg/compiler/lib/src/common/tasks.dart
diff --git a/pkg/compiler/lib/src/common/tasks.dart b/pkg/compiler/lib/src/common/tasks.dart
index 1cc39025be698e09f97b04ce514f482553f9aa50..32966df50b3fbdd936ed8d9df26cd518ff3eba15 100644
--- a/pkg/compiler/lib/src/common/tasks.dart
+++ b/pkg/compiler/lib/src/common/tasks.dart
@@ -24,15 +24,22 @@ class CompilerTask {
   final Compiler compiler;
   final Stopwatch watch;
   UserTag profilerTag;
+  final Map<String, GenericTask> _subtasks = <String, GenericTask>{};
 
   CompilerTask(Compiler compiler)
       : this.compiler = compiler,
         watch = (compiler.verbose) ? new Stopwatch() : null;
 
   String get name => "Unknown task '${this.runtimeType}'";
-  int get timing => (watch != null) ? watch.elapsedMilliseconds : 0;
 
-  int get timingMicroseconds => (watch != null) ? watch.elapsedMicroseconds : 0;
+  int get timing {
+    if (watch == null) return 0;
+    int total = watch.elapsedMilliseconds;
+    for (GenericTask subtask in _subtasks.values) {
+      total += subtask.timing;
+    }
+    return total;
+  }
 
   UserTag getProfilerTag() {
     if (profilerTag == null) profilerTag = new UserTag(name);
@@ -61,6 +68,22 @@ class CompilerTask {
   measureElement(Element element, action()) {
     compiler.withCurrentElement(element, () => measure(action));
   }
+
+  /// Measure the time spent in [action] (if in verbose mode) and accumulate it
+  /// under a subtask with the given name.
+  measureSubtask(String name, action()) {
+    if (watch == null) return action();
+    // Use a nested CompilerTask for the measurement to ensure nested [measure]
+    // calls work correctly. The subtasks will never themselves have nested
+    // subtasks because they are not accessible outside.
+    GenericTask subtask = _subtasks.putIfAbsent(name,
+        () => new GenericTask(name, compiler));
+    return subtask.measure(action);
+  }
+
+  Iterable<String> get subtasks => _subtasks.keys;
+
+  int getSubtaskTime(String subtask) => _subtasks[subtask].timing;
 }
 
 class GenericTask extends CompilerTask {