feat(Scope): Instrument Scope to use User tags in Dart Obervatory

Closes #1138
feat(benchmark): calculate coefficient of variation
refactor(benchmark): reduce complexity, and move formatting of values into template
refactor(benchmark): reduce code redundancy for statistics calculations
feat(benchmark): improve layout of data by moving averages to dedicated row
test(annotion_src_spec): re-enable tests failing due to dartbug 19177

It has been fixed in 1.5.0-dev.4.5

Closes #1150
chore(transformers): use dartSdkDirectory from code_transformers

Closes #1143
feat(mock): Add timer queue checks in mock zone

Closes #1157
fix(component factory): Only create a single ShadowDomComponentFactory
feat(cache): Move cache out of core, add a CacheRegister
feat(cache): Add existing caches to CacheRegister

Closes #1165
fix(cache): Do not export the Cache symbol.

We did not before, don't have a good reason to export it and
it causes collisons with other packages.
feat(travis): Run against g3v1x as well