Add SourceLocationMixin and SourceLocationBase.

Add SourceLocationMixin and SourceLocationBase.

This allows FileLocation to avoid extending SourceLocation at all, which
avoids unused line, column, and sourceUrl fields. This produces a speed
improvement of approximately 5% in the YAML parser, and will likely do
more in code that uses locations more heavily relative to spans.

R=rnystrom@google.com

Committed: https://github.com/dart-lang/source_span/commit/0ca6f8032e0f51e806cbb1e540fccd661c82e77a

[Bob Nystrom, 2015-09-02 19:39:50]

lgtm

https://codereview.chromium.org/1307123004/diff/20001/lib/src/location_mixin....
File lib/src/location_mixin.dart (right):

https://codereview.chromium.org/1307123004/diff/20001/lib/src/location_mixin....
lib/src/location_mixin.dart:43: other is SourceLocation && sourceUrl ==
other.sourceUrl &&
Split after the first "&&" too.

[nweiz, 2015-09-02 20:31:57]

Code review changes

[nweiz, 2015-09-02 20:32:06]

Committed patchset #3 (id:40001) manually as
0ca6f8032e0f51e806cbb1e540fccd661c82e77a (presubmit successful).

[nweiz, 2015-09-02 20:33:05]

https://codereview.chromium.org/1307123004/diff/20001/lib/src/location_mixin....
File lib/src/location_mixin.dart (right):

https://codereview.chromium.org/1307123004/diff/20001/lib/src/location_mixin....
lib/src/location_mixin.dart:43: other is SourceLocation && sourceUrl ==
other.sourceUrl &&
On 2015/09/02 19:39:50, Bob Nystrom wrote:
> Split after the first "&&" too.

Done.