[kernel] Only add metadata if there's at least one annotation

[kernel] Only add metadata if there's at least one annotation.

Currently we run execute "library.AddFieldMetadata",
"library.AddFunctionMetadata" etc for all fields and methods,
even if they do not contain any annotations
(which is what will eventually be extracted from it if ever used).

This CL changes that to only execute the "AddXMetadata" if there
are any annotations.
This saves the VM from creating strings and fields that aren't really
used anyway, while - as before - returning an empty array when
answering a request for metadata for something without any.

BUG=
R=kmillikin@google.com

Committed: https://github.com/dart-lang/sdk/commit/b0de84343a61b52babb70059b0e2c34984379880

[jensj, 2017-07-11 08:00:00]

Description was changed from

==========
[kernel] Only add metadata if there's at least one annotation

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

to

==========
[kernel] Only add metadata if there's at least one annotation.

Currently we run execute "library.AddFieldMetadata",
"library.AddFunctionMetadata" etc for all fields and methods,
even if they do not contain any annotations
(which is what will eventually be extracted from it if ever used).

This CL changes that to only execute the "AddXMetadata" if there
are any annotations.
This saves the VM from creating strings and fields that aren't really
used anyway, while - as before - returning an empty array when
answering a request for metadata for something without any.

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

[jensj, 2017-07-11 08:00:00]

jensj@google.com changed reviewers:
+ kmillikin@google.com

[jensj, 2017-07-11 08:02:07]

I expect this to give a (slight) performance boost, though my attempt to submit
to golem apparently hasn't worked.
As anecdotal evidence on a single run of the tests with and without this patch,
the results was
with:
[18:12 | 100% | +15829 | -    0]

without:
[20:43 | 100% | +15829 | -    0]

It should probably be taken with a grain of salt though...

[Kevin Millikin (Google), 2017-07-11 08:37:10]

LGTM.

[jensj, 2017-07-11 08:40:55]

Description was changed from

==========
[kernel] Only add metadata if there's at least one annotation.

Currently we run execute "library.AddFieldMetadata",
"library.AddFunctionMetadata" etc for all fields and methods,
even if they do not contain any annotations
(which is what will eventually be extracted from it if ever used).

This CL changes that to only execute the "AddXMetadata" if there
are any annotations.
This saves the VM from creating strings and fields that aren't really
used anyway, while - as before - returning an empty array when
answering a request for metadata for something without any.

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

to

==========
[kernel] Only add metadata if there's at least one annotation.

Currently we run execute "library.AddFieldMetadata",
"library.AddFunctionMetadata" etc for all fields and methods,
even if they do not contain any annotations
(which is what will eventually be extracted from it if ever used).

This CL changes that to only execute the "AddXMetadata" if there
are any annotations.
This saves the VM from creating strings and fields that aren't really
used anyway, while - as before - returning an empty array when
answering a request for metadata for something without any.

BUG=
R=kmillikin@google.com

Committed:
https://github.com/dart-lang/sdk/commit/b0de84343a61b52babb70059b0e2c34984379880
==========

[jensj, 2017-07-11 08:40:56]

Committed patchset #1 (id:1) manually as
b0de84343a61b52babb70059b0e2c34984379880 (presubmit successful).