Move dart2js from sdk/lib/_internal/compiler to pkg/compiler

Move dart2js from sdk/lib/_internal/compiler to pkg/compiler

BUG=

Committed: https://code.google.com/p/dart/source/detail?r=41514

[Johnni Winther, 2014-11-05 08:38:36]

johnniwinther@google.com changed reviewers:
+ floitsch@google.com

[Johnni Winther, 2014-11-05 08:38:41]

Reviewed in:

Part 1: https://codereview.chromium.org/687973002/
Part 2: https://codereview.chromium.org/686113002/
Part 3: https://codereview.chromium.org/692513002/

[Johnni Winther, 2014-11-05 08:59:33]

Committed patchset #1 (id:1) manually as 41514 (presubmit successful).

[ahe, 2014-11-05 11:02:51]

ahe@google.com changed reviewers:
+ ahe@google.com

[ahe, 2014-11-05 11:02:55]

LGTM!

git blame appears to be able to find the history of these files. Also, using:

  git log --follow pkg/compiler/lib/compiler.dart

I can follow the history all the way back to when I committed this file using
the name "frog/leg/api.dart"
(https://code.google.com/p/dart/source/detail?r=5168).