Refactoring docgen to make it more unit testable.

Refactoring docgen to make it more unit testable. 


broke up a few other functions to be smaller and only do one thing (mostly).


separated documentLibraries into 3 smaller functions that returns things so that it can be unit tested.

BUG=
R=efortuna@google.com

Committed: https://code.google.com/p/dart/source/detail?r=24486

[Emily Fortuna, 2013-06-26 19:16:43]

lgtm

https://codereview.chromium.org/17893008/diff/1/pkg/docgen/lib/docgen.dart
File pkg/docgen/lib/docgen.dart (right):

https://codereview.chromium.org/17893008/diff/1/pkg/docgen/lib/docgen.dart#ne...
pkg/docgen/lib/docgen.dart:137: void analyzeMirrors(MirrorSystem mirrorSystem) {
consider renaming to something like "setLibraries" or something in keeping with
what is actually happening in this function. Disregard if you disagree

[janicejl, 2013-06-26 20:09:01]

Committed patchset #1 manually as r24486 (presubmit successful).