Optimize LineInfo.getLocation().

Optimize LineInfo.getLocation().

Three simple optimizations:

1. Do a binary search through _lineStarts to find the line instead of linear.
2. Store the last result and see if the offset starts there or later. If so, skip leading lines when searching.
3. See if the current offset is on the same line as the last result and exit early if so.

On my benchmark test for the formatter, this reduced it from 13.23ms to 7.57ms.

R=brianwilkerson@google.com

Committed: https://code.google.com/p/dart/source/detail?r=41452

[Bob Nystrom, 2014-10-31 20:28:33]

rnystrom@google.com changed reviewers:
+ brianwilkerson@google.com

[Bob Nystrom, 2014-10-31 20:28:34]

I just changed the generated Dart file here. Is that OK?

Thanks!

- bob

[Brian Wilkerson, 2014-10-31 21:32:26]

LGTM

> I just changed the generated Dart file here. Is that OK?

Yes! We are no longer generating the files, so hand edits are fine.

[Bob Nystrom, 2014-10-31 21:49:20]

Committed patchset #1 (id:1) manually as 41452 (presubmit successful).

[Bob Nystrom, 2014-10-31 21:49:26]

On 2014/10/31 21:32:26, Brian Wilkerson wrote:
> LGTM
> 
> > I just changed the generated Dart file here. Is that OK?
> 
> Yes! We are no longer generating the files, so hand edits are fine.

\o/

I didn't change the version in the pubspec. Is that OK?