feat(metadata extractor): Cache the fieldMetadataExtractor for greater performance

Dartium tests run in 7.6s; down from 18.2s.
dart2js on Chrome runs in 2m instead of 3m
fix(export): Add missing NgController to angualr.dart
test(ng_model): detect browsers that do not support `simulateTypingText`

Detect browsers that do not support `simulateTypingText` and skip tests
that rely on it.

Closes #814