Use shorter DartElementLocation.

Use shorter DartElementLocation.

This improves analyzer + analysis_server analysis time from 21841 ms to 19839 ms.
I.e. about 9% faster.

However it is still 25% slower than without index at all - 15593 ms.

R=brianwilkerson@google.com
BUG=

Committed: https://code.google.com/p/dart/source/detail?r=41807

[Brian Wilkerson, 2014-11-18 15:11:23]

I'm concerned if we don't need to support HTML or NAME referenced before
committing this, but if that's really the case, LGTM.

https://codereview.chromium.org/738673002/diff/1/pkg/analysis_server/lib/src/...
File pkg/analysis_server/lib/src/services/index/store/codec.dart (right):

https://codereview.chromium.org/738673002/diff/1/pkg/analysis_server/lib/src/...
pkg/analysis_server/lib/src/services/index/store/codec.dart:111: //
TODO(scheglov) support for KIND_HTML ?
And KIND_NAME.

https://codereview.chromium.org/738673002/diff/1/pkg/analysis_server/lib/src/...
pkg/analysis_server/lib/src/services/index/store/codec.dart:171: int nameOffset
= location.nameOffset;
Do we need to ensure that the name offset is non-negative, or do we produce a
unique offset for every kind of element?

https://codereview.chromium.org/738673002/diff/1/pkg/analyzer/lib/src/generat...
File pkg/analyzer/lib/src/generated/element.dart (right):

https://codereview.chromium.org/738673002/diff/1/pkg/analyzer/lib/src/generat...
pkg/analyzer/lib/src/generated/element.dart:3570: // TODO(scheglov) add separate
DartElementImpl
I don't know what that means.

https://codereview.chromium.org/738673002/diff/1/pkg/analyzer/lib/src/generat...
pkg/analyzer/lib/src/generated/element.dart:8522: ElementImpl
_findElementAt(CompilationUnitElement unit, int offset,
Seems like this should either be moved to
CompilationUnitElementImpl.getChildElement(int offset, ElementKind kind) or
encapsulated in the class ElementLocator (see comment below) and inlined above.

https://codereview.chromium.org/738673002/diff/1/pkg/analyzer/lib/src/generat...
pkg/analyzer/lib/src/generated/element.dart:12419: class _FindElementAt extends
GeneralizingElementVisitor {
I'm not sure why this is a private class. Seems like it ought to be a general
purpose class similar to NodeLocator (perhaps named ElementLocator) with a 
utility method that handles catching the exception.

[Brian Wilkerson, 2014-11-18 16:16:06]

LGTM with suggested changes in a follow-on CL.

[scheglov, 2014-11-18 16:21:20]

Committed patchset #1 (id:1) manually as 41807 (presubmit successful).