Native abstract classes may be 'instantiated'

Native abstract classes may be instantiated as a proxy for undeclared native subclasses.

Native classes can have subclasses that are not declared to the program, for example, some browsers have subclasses of HTMLElement that are not present on other browsers.  Instances of these subclasses are treated as instances of the known class (HTMLElement).

What this means is that abstract native classes can appear to have instances, so abstract native classes can appear to be instantiated.

Committed: https://code.google.com/p/dart/source/detail?r=27314

[sra1, 2013-09-09 22:21:49]

Committed patchset #1 manually as r27314 (presubmit successful).

[sra1, 2013-09-09 22:22:12]

TBR=ngeoffray

This fixes issue 12556

[ngeoffray, 2013-09-10 11:55:37]

LGTM

https://codereview.chromium.org/23600020/diff/5001/sdk/lib/_internal/compiler...
File sdk/lib/_internal/compiler/implementation/enqueue.dart (right):

https://codereview.chromium.org/23600020/diff/5001/sdk/lib/_internal/compiler...
sdk/lib/_internal/compiler/implementation/enqueue.dart:125: || cls.isNative()) {
Could we avoid marking the native classes abstract instead?