Make the VM's dart:core and dart:async library patches clean.

sdk/lib/core/errors.dart

Index: sdk/lib/core/errors.dart
diff --git a/sdk/lib/core/errors.dart b/sdk/lib/core/errors.dart
index c11ea2e1a97da25e0c73490a216d7ec025492dc6..92a07a6dab4feb6904f679bd97e0707ba12fae7f 100644
--- a/sdk/lib/core/errors.dart
+++ b/sdk/lib/core/errors.dart
@@ -414,6 +414,9 @@ class IndexError extends ArgumentError implements RangeError {
  */
 class FallThroughError extends Error {
   FallThroughError();
+
+  // TODO: Doc comment please.
+  external String toString();

[Lasse Reichstein Nielsen, 2016/12/08 12:25:32]

Here I would actually prefer each implementation to have their own subclass
instead of patching the toString of the general FallThroughError.

If only the VM changes the toString, only it needs to subclass.

[Lasse Reichstein Nielsen, 2016/12/08 12:26:38]

I can see that that is a more complex change, because you would also need to
change the constructor used everywhere in the VM, so it's OK to keep this for
now, and we can see if we can fix it up later.

[Kevin Millikin (Google), 2016/12/09 08:38:59]

OK.  I will make an issue to track this and other cleanups.

 }
 
 /**
@@ -422,7 +425,9 @@ class FallThroughError extends Error {
 class AbstractClassInstantiationError extends Error {
   final String _className;
   AbstractClassInstantiationError(String this._className);

[Lasse Reichstein Nielsen, 2016/12/08 12:25:32]

Ick. This exposes a private name in the DartDoc. Should at least be

AbstractClassInstantiationError(String className) : _className = className;

[floitsch, 2016/12/08 12:30:46]

Alternatively, dartdoc could try to be clever about this.
It's a very common pattern, and not being able to write the shorter version just
because of dartdoc is annoying.

[Kevin Millikin (Google), 2016/12/09 08:38:59]

I'll adopt Lasse's suggestion.

-  String toString() => "Cannot instantiate abstract class: '$_className'";
+
+  // TODO: Doc comment please.
+  external String toString();

[Lasse Reichstein Nielsen, 2016/12/08 12:25:32]

Again, I'd prefer an implementation specific subclass.

[Kevin Millikin (Google), 2016/12/09 08:38:59]

Acknowledged.

 }
 
 
@@ -459,16 +464,11 @@ class NoSuchMethodError extends Error {
    * the signature of the method that would have been called if the parameters
    * had matched.
    */
-  NoSuchMethodError(Object receiver,
-                    Symbol memberName,
-                    List positionalArguments,
-                    Map<Symbol ,dynamic> namedArguments,
-                    [List existingArgumentNames = null])
-      : _receiver = receiver,
-        _memberName = memberName,
-        _arguments = positionalArguments,
-        _namedArguments = namedArguments,
-        _existingArgumentNames = existingArgumentNames;
+  external NoSuchMethodError(Object receiver,
+                             Symbol memberName,
+                             List positionalArguments,
+                             Map<Symbol, dynamic> namedArguments,
+                             [List existingArgumentNames = null]);
 
   external String toString();
 }