dart2js: Measure time of individual optimization passes.

pkg/compiler/lib/src/apiimpl.dart

Index: pkg/compiler/lib/src/apiimpl.dart
diff --git a/pkg/compiler/lib/src/apiimpl.dart b/pkg/compiler/lib/src/apiimpl.dart
index 357404f148434a059705d2161a66003007fa3e7e..d33b292ab2d93eea157d5c0231dacb70bfb69c52 100644
--- a/pkg/compiler/lib/src/apiimpl.dart
+++ b/pkg/compiler/lib/src/apiimpl.dart
@@ -455,6 +455,10 @@ class Compiler extends leg.Compiler {
           if (elapsed != 0) {
             cumulated += elapsed;
             log('${task.name} took ${elapsed}msec');
+            for (String subtask in task.subtasks) {
+              int subtime = task.getSubtaskTime(subtask);
+              log('${task.name} > $subtask took ${subtime}msec');
+            }
           }
         }
         int total = totalCompileTime.elapsedMilliseconds;