MD Settings: Fix scroll to section

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 130a2881cdca9fca8e0c2f5934194daa3c515c59..ce1e943f7f4eb4ace523905e6a708e337ecefdac 100644
--- a/chrome/browser/resources/settings/settings_page/main_page_behavior.js
+++ b/chrome/browser/resources/settings/settings_page/main_page_behavior.js
@@ -346,7 +346,7 @@ var RoutableBehaviorImpl = {
       if (!element)
         return;
 
-      if (element.parentNode.host.scrollHeight == 0) {
+      if (this.scrollHeight == 0) {
         setTimeout(pollForScrollHeight.bind(this), 100);
         return;
       }
@@ -380,7 +380,7 @@ var RoutableBehaviorImpl = {
       var section = this.getSection_(newRoute.section);
       if (section)
         this.expandSection(section);
-    } else if (newRoute && newRoute.section) {
+    } else if (newRoute && newRoute.section && !oldRouteIsSubpage) {

[dschuyler, 2016/06/06 23:51:42]

What is this addition addressing?

[michaelpg, 2016/06/07 02:55:05]

Warning: wall of text that I'm publishing for my notes, probably not worth
reading because implementing the very last line may nullify everything else.

here, oldRouteIsSubpage implies newRouteIsSubpage which implies newRoute.section
== oldRoute.section

so: old route and new route are both subpages within the same section, so it
does NOT make sense to change the scroll position (ie, we shouldn't[1] change
the scroll position of the page from whatever it was before entering the first
subpage).

[1] it doesn't actually, because of implementation details elsewhere, so this is
just preventative (and a very minor optimization) rather than a bug fix.

Equivalently, we shouldn't scroll to the section when showing a subpage
(!oldRouteIsSubpage also implies !newRouteIsSubpage due to 378-379). We may want
to add this behavior, but we should do it at line 380 where it belongs.

However, there's another fix we need: 377 should also scroll to the section IF
we got here by clicking a menu entry, or a link to some other section, but NOT
if we used the back button or just hit the back arrow in the subpage... crap.

[dschuyler, 2016/06/08 00:35:05]

That's a lot of indirect logic for folks following along at home, please
consider one of the following:
- rework the logic flow here (lines 374 to 385) to make it easier to follow
- or add a bug with your notes above and comment around line 374 that this logic
should be reworked, referencing the new bug.

       this.scrollToSection_();
     }
   },