fix #29789, avoid unneccessary dcalls and checks in dart:_runtime

fix #29789, avoid unneccessary dcalls and checks in dart:_runtime

R=vsm@google.com

Committed: https://github.com/dart-lang/sdk/commit/e79fbd167b24a515cde63ff37db5e410f053ad11

[Jennifer Messerly, 2017-06-10 00:43:08]

jmesserly@google.com changed reviewers:
+ vsm@google.com

[Jennifer Messerly, 2017-06-10 00:43:09]

https://codereview.chromium.org/2932043003

https://codereview.chromium.org/2932043003/diff/1/pkg/dev_compiler/tool/input...
File pkg/dev_compiler/tool/input_sdk/private/ddc_runtime/types.dart (right):

https://codereview.chromium.org/2932043003/diff/1/pkg/dev_compiler/tool/input...
pkg/dev_compiler/tool/input_sdk/private/ddc_runtime/types.dart:437: return
_functionType == null ? _functionType = _closure() : _functionType;
was getting some suboptimal code out of ??= so I left it this way.

[vsm, 2017-06-12 19:41:18]

lgtm

[Jennifer Messerly, 2017-06-12 22:44:55]

Description was changed from

==========
fix #29789, avoid unneccessary dcalls and checks in dart:_runtime
==========

to

==========
fix #29789, avoid unneccessary dcalls and checks in dart:_runtime

R=vsm@google.com

Committed:
https://github.com/dart-lang/sdk/commit/e79fbd167b24a515cde63ff37db5e410f053ad11
==========

[Jennifer Messerly, 2017-06-12 22:44:56]

Committed patchset #3 (id:20001) manually as
e79fbd167b24a515cde63ff37db5e410f053ad11 (presubmit successful).