Compile print_preview, part 2: reduce down to 260 errors

chrome/browser/resources/print_preview/component.js

Index: chrome/browser/resources/print_preview/component.js
diff --git a/chrome/browser/resources/print_preview/component.js b/chrome/browser/resources/print_preview/component.js
index 2baa4c8f89439419ec04d462c24a98593355443c..8dce970a6df15dc028fcc30f4aab95d548f6f052 100644
--- a/chrome/browser/resources/print_preview/component.js
+++ b/chrome/browser/resources/print_preview/component.js
@@ -31,7 +31,7 @@ cr.define('print_preview', function() {
 
     /**
      * Child components of the component.
-     * @type {Array.<print_preview.Component>}
+     * @type {Array.<!print_preview.Component>}
      * @private
      */
     this.children_ = [];
@@ -119,7 +119,7 @@ cr.define('print_preview', function() {
     },
 
     /**
-     * @param {print_preview.Component} child Component to add as a child of
+     * @param {!print_preview.Component} child Component to add as a child of
      *     this component.
      */
     addChild: function(child) {
@@ -154,10 +154,10 @@ cr.define('print_preview', function() {
      * @param {string} query Selector query to select an element starting from
      *     the component's root element using a depth first search for the first
      *     element that matches the query.
-     * @return {HTMLElement} Element selected by the given query.
+     * @return {!HTMLElement} Element selected by the given query.

[Aleksey Shlyapnikov, 2014/09/19 18:54:42]

Why? This is a generic function and it's not guaranteed that the element we are
looking for is there.

[Vitaly Pavlenko, 2014/09/19 20:33:09]

I tried to add this assert, compile the browser and play around with
print_preview. I haven't found any failures on this assert.

Do you think that instead I should add assert() around all calls to
getChildElement()?

[Aleksey Shlyapnikov, 2014/09/19 20:48:59]

So with no assert and @return {HTMLElement} declaration Closure compiler
complains on every getChildElement's call site?

Can you leave a TODO here (on my name) to check all call sites and rename this
function to something like getRequiredChildElement?

[Vitaly Pavlenko, 2014/09/19 21:12:53]

Yes, without this assert you get 40 errors like this:
##
/usr/local/google/home/vitalyp/src/chrome/browser/resources/print_preview/search/destination_search.js:441:
ERROR - actual parameter 1 of setIsVisible does not match formal parameter
## found   : (HTMLElement|null)
## required: HTMLElement
##       setIsVisible(this.getChildElement('.cloud-list'), loggedIn);
##                    ^

TODO is inserted.

      */
     getChildElement: function(query) {
-      return this.element_.querySelector(query);
+      return assert(this.element_.querySelector(query));
     },
 
     /**