Add StackTrace.current getter.

sdk/lib/_internal/js_runtime/lib/core_patch.dart

Index: sdk/lib/_internal/js_runtime/lib/core_patch.dart
diff --git a/sdk/lib/_internal/js_runtime/lib/core_patch.dart b/sdk/lib/_internal/js_runtime/lib/core_patch.dart
index 301517ee669f5a532008375f12048c4f37bc0ba0..b448327caa13ab4f816e461a623b30eb75068822 100644
--- a/sdk/lib/_internal/js_runtime/lib/core_patch.dart
+++ b/sdk/lib/_internal/js_runtime/lib/core_patch.dart
@@ -671,3 +671,22 @@ class _Resource implements Resource {
     });
   }
 }
+
+@patch
+class StackTrace {
+  @patch static StackTrace get current {
+    var error = JS("Object", "new Error()");

[sra1, 2015/11/17 19:11:37]

Don't use "Object".
That means any subclass of Object.
"=Object" means a plain JavaScript object, which is better but not really true.

It is best to use an empty spec, which means dynamic, but not a type new to the
program (so not pulling in all of IndexDB etc). This is OK since all we do is
compare to null, other JS code and call wrapping functions.

Use single quotes throughout.

[Lasse Reichstein Nielsen, 2015/11/18 10:11:39]

Done

+    var stack = JS("Object", "#.stack", error);

[sra1, 2015/11/17 19:11:37]

The type here should be 'String|Null'.
That will give better type inference for StackTrace.fromString(stack)

[Lasse Reichstein Nielsen, 2015/11/18 10:11:39]

Done.

+    if (stack != null) return new StackTrace.fromString(stack);

[sra1, 2015/11/17 19:11:37]

It would be a little safer for this test to be 'is String'

[Lasse Reichstein Nielsen, 2015/11/18 10:11:39]

Done

+    if (JS("Object", "Error.captureStackTrace") != null) {
+      JS("void", "Error.captureStackTrace(#)", error);
+      var stack = JS("Object", "#.stack", error);

[sra1, 2015/11/17 19:11:37]

'String|Null'

[Lasse Reichstein Nielsen, 2015/11/18 10:11:39]

Done.

[Lasse Reichstein Nielsen, 2015/11/18 10:11:39]

Done.

+      if (stack != null) return new StackTrace.fromString(stack);
+    }
+    try {
+      throw 0;

[floitsch, 2015/11/16 19:30:21]

Which browsers still need this?

[Lasse Reichstein Nielsen, 2015/11/17 13:18:53]

IE11 as far as I can see. Don't know about Safari or MS Edge (can't check).

+    } catch (_, stackTrace) {
+      return stackTrace;

[sra1, 2015/11/17 19:11:37]

This there a measurable performance benefit over simply having this code?
The above code is a but fussy, so I'd rather have the fussiness in one place
unless the benefit is noticeable.

[Lasse Reichstein Nielsen, 2015/11/18 10:11:39]

It's not about performance, but about not interfering with "break on throw"
debugging if it can be avoided.

It's basically a response to https://github.com/dart-lang/sdk/issues/24922

+    }
+  }
+}