Prevent ExtendableMessageEvent.data from thwarting DOM tree-shaking

Prevent ExtendableMessageEvent.data from thwarting DOM tree-shaking

We can't have the [data] and [source] getters typed as Object.
This causes it to appear that all DOM types are instantiated.

I have modelled the annotations after the same getters from
MessageEvent.

TBR=jacobr@google.com

BUG=

Committed: https://github.com/dart-lang/sdk/commit/ca3d90c4cd7155709a7836d0830b1f712925a8cd

[sra1, 2017-05-12 02:30:58]

sra@google.com changed reviewers:
+ terry@google.com

[sra1, 2017-05-12 02:30:58]

Reduces swarm by 70k.

[sra1, 2017-05-12 02:31:31]

Description was changed from

==========
Prevent ExtendableMessageEvent.data from thwarting DOM tree-shaking

We can't have the [data] and [source] getters typed as Object.
This causes it to appear that all DOM types are instantiated.

I have modelled the annotations after the same getters from
MessageEvent.

TBR=jacobr@google.com

BUG=
==========

to

==========
Prevent ExtendableMessageEvent.data from thwarting DOM tree-shaking

We can't have the [data] and [source] getters typed as Object.
This causes it to appear that all DOM types are instantiated.

I have modelled the annotations after the same getters from
MessageEvent.

TBR=jacobr@google.com

BUG=

Committed:
https://github.com/dart-lang/sdk/commit/ca3d90c4cd7155709a7836d0830b1f712925a8cd
==========

[sra1, 2017-05-12 02:31:32]

Committed patchset #1 (id:1) manually as
ca3d90c4cd7155709a7836d0830b1f712925a8cd (presubmit successful).

[Jacob, 2017-05-12 02:41:36]

lgtm

https://codereview.chromium.org/2879763002/diff/1/tools/dom/scripts/dartmetad...
File tools/dom/scripts/dartmetadata.py (right):

https://codereview.chromium.org/2879763002/diff/1/tools/dom/scripts/dartmetad...
tools/dom/scripts/dartmetadata.py:163: # the JavaScript wire type into a Dart
type.
Yeah this is most likely busted as is.