feat(benchmark): add automatic gc before each test

Also included is a script to launch Chrome Canary with the appropriate flag to
enable manual garbage collection.

Closes #1133
docs(developer): fix typo in developer.md

Changed instance of "xhange" to "change"
perf(compiler): +6% Pre-compute ViewFactories, styles for components.

This sped up the TreeComponent benchmark by 6%.

Closes #1134
benchmark(TreeComponent): Update for watchAST and disable ElementProbe.
test(benchmark): add test runner and stubs for bp.js

This commit adds a karma setup with a spec file for bp.js, and
has refactored bp.js to expose all functions on a global "bp" object.

Behavior of functions hasn't changed, other than to remove some
duplication of code regarding adding buttons to the DOM.
test(benchmark): add ability to run 25 iterations of test, sampling only the last 20

This commit also breaks the functionality into smaller, more testable functions,
and adds some basic tests for the benchmarking too.
feat(Scope): Use VmTurnZone.onScheduleMicrotask in Scope

BREAKING CHANGE:

Previously a micro task registered in flush phase would cause a new
digest cycle after the current digest cycle. The new behavior
will cause an error.

Closes #984
fix(scope): Use runAsync for microtasks in digest.

BREAKING CHANGE:

Microtasks scheduled in flush will process in current cycle, but they 
are not allowed to do model changes.

Microtasks scheduled in digest will be executed in digest, counting
towards the ScopeDigestTTL.
feat(benchmark): add ability to adjust sample quantity

Move creation of HTML elements into tree.html where possible.

Improve styling with bootstrap lib plus basic structuring of content.
feat(benchmark): record gc time for each test run
perf(ChangeDetector): lazy initialize DuplicateMap

This slightly reduces number of Maps in the system.
perf(ChangeDetector): create _EvalWatchRecord#namedArgs lazily

This change reduces the number of Maps in the heap on binding heavy views by 30%.
perf: use HashMaps instead of LinkedHashMaps where possible
feat(benchmark): change samples input type from range to text
feat(benchmark): improve sampling UI

 * Increase default sample from 10 to 20
 * Convert sample adjuster from range to input
 * Make sample list scrollable after 250px height
feat(Scope): Instrument Scope to use User tags in Dart Obervatory