[MD settings] remove label float from dropdowns so that they center correctly

chrome/browser/resources/settings/search_page/search_page.html

Index: chrome/browser/resources/settings/search_page/search_page.html
diff --git a/chrome/browser/resources/settings/search_page/search_page.html b/chrome/browser/resources/settings/search_page/search_page.html
index 5f0d6c0c4b9c6c103abd1d35f67289e6d0858694..cc4f0495dea4bdf8f3cbb6fc6113bb5d9df0b901 100644
--- a/chrome/browser/resources/settings/search_page/search_page.html
+++ b/chrome/browser/resources/settings/search_page/search_page.html
@@ -19,7 +19,7 @@
       <neon-animatable id="main">
         <div class="settings-box first">
           <p class="start">$i18n{searchExplanation}</p>
-          <paper-dropdown-menu vertical-align="auto">
+          <paper-dropdown-menu vertical-align="auto" no-label-float>

[stevenjb, 2016/07/29 16:21:08]

I am wondering if we could do something like this in the shared CSS so that we
do not need to add this everywhere (values copied from
paper-dropdown-menu-light.html):

paper-dropdown-menu {
  --paper-dropdown-menu-input {
    padding-top: 0;
  }
  --paper-dropdown-menu-label {
    top: 8px;
  }
  --paper-dropdown-menu-icon {
    margin-top: 0px;
  }
}

The disadvantage is that we would have to maintain that styling. Also, there are
a couple of CSS rules that do not have associated CSS vars; I don't think they
will matter, but they might?

+michaelpg@, WDYT?

[michaelpg, 2016/07/29 17:40:36]

seems like no-label-float does a variety of magical[1] things including
affecting the ripple[2] and things dependent on state[3][4].

[1]
https://github.com/PolymerElements/paper-dropdown-menu/blob/master/paper-drop...
[2]
https://github.com/PolymerElements/paper-dropdown-menu/blob/master/paper-drop...
[3]
https://github.com/PolymerElements/paper-input/blob/master/paper-input-contai...
[4]
https://github.com/PolymerElements/paper-input/blob/master/paper-input-contai...

so... if we don't use a label, no-label-float seems worthwhile.

[stevenjb, 2016/07/29 17:45:34]

OK. Wish there were a way to change the default. Oh well.

             <paper-listbox class="dropdown-content"
                 selected="[[getSelectedSearchEngineIndex_(searchEngines_)]]"
                 on-iron-select="onIronSelect_">