Manage 'libraries containing part' in DartWorkManager.

Manage 'libraries containing part' in DartWorkManager.

It is on the couple critical paths:
1. getErrors()
2. SearchEngine.

The SearchEngine is used in both search itself and by completion.
Without this change search has n^2 complexity, where `n` is the number of targets.

Statistics for search shows more than 10x performance improvement.
Before: 70 ms (analyzer), 230 ms (analyzer + dart2js).
After: 6 ms (analyzer), 17 ms (analyzer + dart2js).

R=brianwilkerson@google.com
BUG=

Committed: https://github.com/dart-lang/sdk/commit/224734d4e41400d256ac0106302674351aa37bd9

[Brian Wilkerson, 2015-05-22 16:05:42]

LGTM

It's not surprising that we need this. We needed it in the old system for
performance too.

https://codereview.chromium.org/1152773002/diff/1/pkg/analyzer/lib/src/task/d...
File pkg/analyzer/lib/src/task/dart_work_manager.dart (right):

https://codereview.chromium.org/1152773002/diff/1/pkg/analyzer/lib/src/task/d...
pkg/analyzer/lib/src/task/dart_work_manager.dart:72: final HashMap<Source,
List<Source>> libraryPartsMap =
Aren't we already keeping this in the cache? Why would we duplicate the
information?

https://codereview.chromium.org/1152773002/diff/1/pkg/analyzer/lib/src/task/d...
pkg/analyzer/lib/src/task/dart_work_manager.dart:264: libraryPartsMap[library] =
includedParts.toList();
"includedParts" is declared to be a List. Is the declaration wrong or the
"toList" unnecessary?

[scheglov, 2015-05-22 16:21:00]

Committed patchset #1 (id:1) manually as
224734d4e41400d256ac0106302674351aa37bd9 (presubmit successful).