refactor(zone.js): use Object.prototype.toString directly for impro…

…ved tree shakability

These lines were not tree shakable by Closure Compiler because `.toString()` is special cased as a "pure" function eligible to eliminated if it's return value is unused. However `.toString.call` circuments this and makes Closure Compiler think the function may have side effects. Switching to `.toString()` should be fine here as `process.toString()` in Node outputs `[object process]` so this should be safe. Presumably the original motivation for this roundabout approach was for type safety reasons which no longer apply as `_global` is `any`.

packages/zone.js/lib/common/utils.ts

@@ -110,7 +110,7 @@ export const isWebWorker: boolean =
 // this code.
 export const isNode: boolean =
     (!('nw' in _global) && typeof _global.process !== 'undefined' &&
-     {}.toString.call(_global.process) === '[object process]');
+     _global.process.toString() === '[object process]');
 
 export const isBrowser: boolean =
     !isNode && !isWebWorker && !!(isWindowExists && internalWindow['HTMLElement']);
@@ -119,7 +119,7 @@ export const isBrowser: boolean =
 // Make sure to access `process` through `_global` so that WebPack does not accidentally browserify
 // this code.
 export const isMix: boolean = typeof _global.process !== 'undefined' &&
-    {}.toString.call(_global.process) === '[object process]' && !isWebWorker &&
+    _global.process.toString() === '[object process]' && !isWebWorker &&
     !!(isWindowExists && internalWindow['HTMLElement']);
 
 const zoneSymbolEventNames: {[eventName: string]: string} = {};