Use Zone to correctly measure async operations.

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 56bf4c153137099d0c4e24ec094dcb31ddca4b0b..cdda6fe01f572fe88f38b12aebd77d0b926cb542 100644
--- a/pkg/compiler/lib/src/apiimpl.dart
+++ b/pkg/compiler/lib/src/apiimpl.dart
@@ -486,7 +486,7 @@ class Compiler extends leg.Compiler {
 
   Future callUserProvider(Uri uri) {
     try {
-      return userProviderTask.measure(() => provider.readFromUri(uri));
+      return userProviderTask.measureIo(() => provider.readFromUri(uri));
     } catch (ex, s) {
       diagnoseCrashInUserCode('Uncaught exception in input provider', ex, s);
       rethrow;
@@ -495,7 +495,7 @@ class Compiler extends leg.Compiler {
 
   Future<Packages> callUserPackagesDiscovery(Uri uri) {
     try {
-      return userPackagesDiscoveryTask.measure(
+      return userPackagesDiscoveryTask.measureIo(
                  () => packagesDiscoveryProvider(uri));
     } catch (ex, s) {
       diagnoseCrashInUserCode('Uncaught exception in package discovery', ex, s);