refactor(perf): use webdriver to execute benchmarks

- use performance log of chromedriver / appium to get timeline data
  for calculating metrics for benchmarks
- change all benchmarks to be made of a standalone application
  and a protractor test that collectes timeline data
- fix and simplify benchmarks
- add dart2js to build
- remove benchpress

Closes #330

modules/core/src/compiler/compiler.js

@@ -36,6 +36,10 @@ export class CompilerCache {
     }
     return result;
   }
+
+  clear() {
+    this._cache = MapWrapper.create();
+  }
 }
 
 /**