Make print interceptable.

sdk/lib/_internal/lib/collection_dev_patch.dart

Index: sdk/lib/_internal/lib/collection_dev_patch.dart
diff --git a/sdk/lib/_internal/lib/collection_dev_patch.dart b/sdk/lib/_internal/lib/collection_dev_patch.dart
index f224f24aab6db81fdd02fe889ed215cbb223c6e5..f7467fd72562765f3afdeafc9f0669ef60bc54d1 100644
--- a/sdk/lib/_internal/lib/collection_dev_patch.dart
+++ b/sdk/lib/_internal/lib/collection_dev_patch.dart
@@ -2,7 +2,45 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+import 'dart:_foreign_helper' show JS;

[ahe, 2013/11/04 09:01:19]

In the future, please do not add dart2js secret implementation details to
libraries that do not need them. In particular, do not import
dart:_foreign_helper.

In this case, you should have written:

import 'dart:_js_helper' show Primitives;

patch void printToConsole(String line) {
  Primitives.printString(line);
}

+
 patch class Symbol implements core.Symbol {
   patch const Symbol(String name)
       : this._name = name;
 }
+
+/**
+  * This is the low-level method that is used to implement
+  * [print]. It is possible to override this function from JavaScript
+  * by defining a function in JavaScript called "dartPrint".
+  */
+patch void printToConsole(String line) {
+  if (JS('bool', r'typeof dartPrint == "function"')) {
+    // Support overriding print from JavaScript.
+    JS('void', r'dartPrint(#)', line);
+    return;
+  }
+
+  // Inside browser or nodejs.
+  if (JS('bool', r'typeof console == "object"') &&
+      JS('bool', r'typeof console.log == "function"')) {
+    JS('void', r'console.log(#)', line);
+    return;
+  }
+
+  // Don't throw inside IE, the console is only defined if dev tools is open.
+  if (JS('bool', r'typeof window == "object"')) {
+    return;
+  }
+
+  // Running in d8, the V8 developer shell, or in Firefox' js-shell.
+  if (JS('bool', r'typeof print == "function"')) {
+    JS('void', r'print(#)', line);
+    return;
+  }
+
+  // This is somewhat nasty, but we don't want to drag in a bunch of
+  // dependencies to handle a situation that cannot happen. So we
+  // avoid using Dart [:throw:] and Dart [toString].
+  JS('void', 'throw "Unable to print message: " + String(#)', line);
+}