Make print interceptable.

sdk/lib/async/zone.dart

Index: sdk/lib/async/zone.dart
diff --git a/sdk/lib/async/zone.dart b/sdk/lib/async/zone.dart
index 80184c2e75e67f00ef01e7c42e0f269589dbd582..b5fa0d183c57553589b900d4cf86a2de94dee88d 100644
--- a/sdk/lib/async/zone.dart
+++ b/sdk/lib/async/zone.dart
@@ -31,6 +31,8 @@ typedef Timer CreateTimerHandler(
 typedef Timer CreatePeriodicTimerHandler(
     Zone self, ZoneDelegate parent, Zone zone,
     Duration period, void f(Timer timer));
+typedef void PrintHandler(
+    Zone self, ZoneDelegate parent, Zone zone, String line);
 typedef Zone ForkHandler(Zone self, ZoneDelegate parent, Zone zone,
                          ZoneSpecification specification,
                          Map<Symbol, dynamic> zoneValues);
@@ -82,6 +84,7 @@ abstract class ZoneSpecification {
                       Duration duration, void f()): null,
     Timer createPeriodicTimer(Zone self, ZoneDelegate parent, Zone zone,
                               Duration period, void f(Timer timer)): null,
+    void print(Zone self, ZoneDelegate parent, Zone zone, String line): null,
     Zone fork(Zone self, ZoneDelegate parent, Zone zone,
               ZoneSpecification specification, Map zoneValues): null
   }) = _ZoneSpecification;
@@ -112,6 +115,7 @@ abstract class ZoneSpecification {
                       Duration duration, void f()): null,
     Timer createPeriodicTimer(Zone self, ZoneDelegate parent, Zone zone,
                               Duration period, void f(Timer timer)): null,
+    void print(Zone self, ZoneDelegate parent, Zone zone, String line): null,
     Zone fork(Zone self, ZoneDelegate parent, Zone zone,
               ZoneSpecification specification,
               Map<Symbol, dynamic> zoneValues): null
@@ -141,6 +145,7 @@ abstract class ZoneSpecification {
       createPeriodicTimer: createPeriodicTimer != null
                            ? createPeriodicTimer
                            : other.createPeriodicTimer,
+      print : print != null ? print : other.print,
       fork: fork != null ? fork : other.fork);
   }
 
@@ -156,6 +161,7 @@ abstract class ZoneSpecification {
   RunAsyncHandler get runAsync;
   CreateTimerHandler get createTimer;
   CreatePeriodicTimerHandler get createPeriodicTimer;
+  PrintHandler get print;
   ForkHandler get fork;
 }
 
@@ -179,6 +185,7 @@ class _ZoneSpecification implements ZoneSpecification {
     this.runAsync: null,
     this.createTimer: null,
     this.createPeriodicTimer: null,
+    this.print: null,
     this.fork: null
   });
 
@@ -195,6 +202,7 @@ class _ZoneSpecification implements ZoneSpecification {
   final /*RunAsyncHandler*/ runAsync;
   final /*CreateTimerHandler*/ createTimer;
   final /*CreatePeriodicTimerHandler*/ createPeriodicTimer;
+  final /*PrintHandler*/ print;
   final /*ForkHandler*/ fork;
 }
 
@@ -224,6 +232,7 @@ abstract class ZoneDelegate {
   void scheduleMicrotask(Zone zone, f());
   Timer createTimer(Zone zone, Duration duration, void f());
   Timer createPeriodicTimer(Zone zone, Duration period, void f(Timer timer));
+  void print(Zone zone, String line);
   Zone fork(Zone zone, ZoneSpecification specification, Map zoneValues);
 }
 
@@ -386,6 +395,11 @@ abstract class Zone {
   Timer createPeriodicTimer(Duration period, void callback(Timer timer));
 
   /**
+   * Prints the given [line].
+   */
+  void print(String line);
+
+  /**
    * The error zone is the one that is responsible for dealing with uncaught
    * errors. Errors are not allowed to cross zones with different error-zones.
    */
@@ -507,6 +521,15 @@ class _ZoneDelegate implements ZoneDelegate {
         parent, new _ZoneDelegate(parent.parent), zone, period, f);
   }
 
+  void print(Zone zone, String line) {
+    _CustomizedZone parent = _degelationTarget;
+    while (parent._specification.print == null) {
+      parent = parent.parent;
+    }
+    (parent._specification.print)(
+        parent, new _ZoneDelegate(parent.parent), zone, line);
+  }
+
   Zone fork(Zone zone, ZoneSpecification specification,
             Map<Symbol, dynamic> zoneValues) {
     _CustomizedZone parent = _degelationTarget;
@@ -651,6 +674,10 @@ class _CustomizedZone implements Zone {
   Timer createPeriodicTimer(Duration duration, void f(Timer timer)) {
     return new _ZoneDelegate(this).createPeriodicTimer(this, duration, f);
   }
+
+  void print(String line) {
+    new _ZoneDelegate(this).print(this, line);
+  }
 }
 
 void _rootHandleUncaughtError(
@@ -735,6 +762,10 @@ Timer _rootCreatePeriodicTimer(
   return _createPeriodicTimer(duration, callback);
 }
 
+void _rootPrint(Zone self, ZoneDelegate parent, Zone zone, String line) {
+  internalPrint(line);
+}
+
 Zone _rootFork(Zone self, ZoneDelegate parent, Zone zone,
                ZoneSpecification specification,
                Map<Symbol, dynamic> zoneValues) {
@@ -767,6 +798,7 @@ const _ROOT_SPECIFICATION = const ZoneSpecification(
   scheduleMicrotask: _rootScheduleMicrotask,
   createTimer: _rootCreateTimer,
   createPeriodicTimer: _rootCreatePeriodicTimer,
+  print: _rootPrint,
   fork: _rootFork
 );