Site Settings Desktop: Implement USB devices section.

chrome/browser/resources/settings/settings_shared_css.html

 <link rel="import" href="chrome://resources/cr_elements/shared_style_css.html">
 <link rel="import" href="/settings_vars_css.html">
 
 <!-- Common styles for Material Design settings. -->
 <dom-module id="settings-shared">
   <template>
     <style include="cr-shared-style">
       h2 {
         align-items: center;
         display: flex;
@@ skipping 326 matching lines @@
         --paper-slider-pin-start-color: var(--google-blue-700);
       }
 
       .favicon-image {
         background-repeat: no-repeat;
         background-size: contain;
         height: 16px;
         width: 16px;
       }
 
+      .site-settings-header {
+        -webkit-margin-start: 20px;
+        margin-bottom: 15px;
+        margin-top: 15px;
+      }

[dschuyler, 2016/08/11 23:28:07]

If this is only used in site settings, please move it to 
where it is used. If it's useful to more than site settings,
please give it a name that is more general.
(This file is intended for classes that are used in several
sections).

[Finnur, 2016/08/12 13:11:25]

Sorry, I interpreted your words at our encounter in LA as an indication that if
a css rule was used in more than one place, it should belong centrally (which I
thought was the settings_shared css). Moved this back.

[dschuyler, 2016/08/12 20:58:48]

Oh, that's correct. If it's used in more places then it should be moved to a 
more central place (such as this file). I didn't mean to contradict that. 
I could have been more clear by saying:

"If this is only used in **protocol_handlers.html**, please move it to 
where it is used. If it's useful to more than **protocol_handlers.html**,
please give it a name that is more general".

The comment about the name is because it would be weird if it were used in
Appearance or Search Engines settings and had the name "site-settings-*".

I see now that this is being added in usb_devices.html in addition to 
protocol_handlers.html. I think I'm fine with any of these: have two copies of
this style class (not ideal, though not terrible); or have a 
site_settings_css.html with the style; or add it to 
settings_shared_css.html with a different name on the class.

[Finnur, 2016/08/15 11:54:33]

Fair enough. I'll leave it as is for now and if I add more instances of this, or
more shared values for Site Settings then I'll consolidate those all into a
separate css file for site_settings.

+
       .search-bubble {
         pointer-events: none;
         position: absolute;
       }
 
       .search-bubble-innards {
         align-items: center;
         background-color: var(--paper-yellow-500);
         border-radius: 2px;
         display: flex;
@@ skipping 12 matching lines @@
         top: 10px;
         width: 10px;
       }
 
       .search-highlight-hit {
         background-color: var(--paper-yellow-500);
       }
     </style>
   </template>
 </dom-module>