test instant subpage load with animation duration 0

chrome/browser/resources/settings/settings_page/main_page_behavior.js

Index: chrome/browser/resources/settings/settings_page/main_page_behavior.js
diff --git a/chrome/browser/resources/settings/settings_page/main_page_behavior.js b/chrome/browser/resources/settings/settings_page/main_page_behavior.js
index 3886816a9110fcb731267fad86474ae00c3b1cf4..3965992010b42f669936fdd76a1979683c839997 100644
--- a/chrome/browser/resources/settings/settings_page/main_page_behavior.js
+++ b/chrome/browser/resources/settings/settings_page/main_page_behavior.js
@@ -36,7 +36,17 @@ var MainPageBehaviorImpl = {
   scroller: null,
 
   listeners: {
-    'neon-animation-finish': 'onNeonAnimationFinish_'
+    'neon-animation-finish': 'onNeonAnimationFinish_',
+    'subpage-expand': 'onSubpageExpand_',
+  },
+
+  onSubpageExpand_: function() {
+    debugger;
+    if (this.oldDuration_) {
+      settings.animation.Timing.DURATION = this.oldDuration_;
+      document.body.querySelector('settings-ui::shadow #container').style.visibility = 'visible';
+      this.oldDuration_ = undefined;
+    }
   },
 
   /** @override */
@@ -94,8 +104,14 @@ var MainPageBehaviorImpl = {
 
     // For previously uncreated pages (including on first load), allow the page
     // to render before scrolling to or expanding the section.
-    if (!oldRoute || this.scrollHeight == 0)
+    if (!oldRoute) {
+      if (newRoute.isSubpage()) {
+        this.oldDuration_ = settings.animation.Timing.DURATION;
+        settings.animation.Timing.DURATION = 0;
+        document.body.querySelector('settings-ui::shadow #container').style.visibility = 'hidden';

[michaelpg, 2017/05/05 20:42:44]

using visibility: hidden instead of display: none so the section still has a
size, otherwise various errors occur because things have no size and
tryTransitionToSection enters an infinite loop

[michaelpg, 2017/05/22 22:10:51]

(Copying scottchen's response to this thread:)
I'm not sure. The code is already too complicated, because we keep adding
conditions that weren't planned for. But you're right that setting the duration
to 0 globally is hacky (and possibly risky if for some reason we don't set it
back).

I wonder if a compromise would be to have the DURATION always start at 0, and
only set DURATION to the normal value upon receiving some event to tell us that
the important stuff on the page has finished loading?

We might still have to fiddle with showing/hiding some things, but maybe
changing the start conditions instead of trying a bunch of async stuff would be
simpler.
Can we simplify your CL with a one-off event we fire that causes settings-ui to
show/hide the container instead of data binding?

+      }
       setTimeout(this.tryTransitionToSection_.bind(this, scrollToSection));
+    }
     else
       this.tryTransitionToSection_(scrollToSection);
   },