docs(angular): adds docs to angular API (#17211)

angular/src/providers/dom-controller.ts

@@ -5,10 +5,18 @@ import { Injectable } from '@angular/core';
 })
 export class DomController {
 
+  /**
+   * Schedules a task to run during the READ phase of the next frame.
+   * This task should only read the DOM, but never modify it.
+   */
   read(cb: RafCallback) {
     getQueue().read(cb);
   }
 
+  /**
+   * Schedules a task to run during the WRITE phase of the next frame.
+   * This task should write the DOM, but never READ it.
+   */
   write(cb: RafCallback) {
     getQueue().write(cb);
   }