MD WebUI: Move some settings CSS to shared_style_css

chrome/browser/resources/settings/settings_root_css.html

+<link rel="import" href="chrome://resources/cr_elements/shared_style_css.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-styles/color.html">
 
 <!-- Common css variables for Material Design settings. -->
-<style is="custom-style">
+<style is="custom-style" include="cr-shared-style">

[dschuyler, 2016/07/21 00:04:48]

Can this include be done elsewhere?

I see now that the comment above is vague. The intention
here was to have a file that had only variables and no
other items. i.e. if none of the variables were used then
the contents (hmm, 'heaviness'?) of the file is essentially
zero.

[stevenjb, 2016/07/21 15:46:31]

So just to be clear, you would advocate for creating shared_root_css.html now,
and including that here instead?

   :root {
     --checkbox-margin-start: 2px;
     --checkbox-size: 16px;
     --checkbox-spacing: 18px;
     --iron-icon-fill-color: var(--paper-grey-600);
     --iron-icon-height: 20px;
     --iron-icon-spacing: 16px;
     --iron-icon-width: 20px;
     --paper-checkbox-label-color: inherit;
     --paper-dialog-color: inherit;
     --paper-icon-button: {
       width: 36px;
       height: 36px;
     };
     --paper-input-max-width: 264px;
     --paper-item: {
       font-size: inherit;
     };
     --paper-radio-button-label-color: inherit;
     --paper-radio-group-item-padding: 0;
 
+    --settings-actionable: var(--cr-actionable);
+
     /* Custom grey for Alan (bettes@). */
     --settings-background-color: rgb(241, 241, 241);
     --settings-secondary: {
       color: var(--paper-grey-600);
       font-weight: 400;
       margin-top: 4px;
     };
     --settings-error-color: var(--paper-red-700);
-    --settings-hover-color: var(--google-grey-300);
 
     /* Some colors use non-MD colors.  These custom colors are specified by
      * UX design (bettes@). */
     --settings-nav-grey: rgb(90, 90, 90);
 
     --settings-page-vertical-margin: 21px;
 
     --settings-row-min-height: 44px;
-    --settings-separator-line: 1px solid rgba(0, 0, 0, 0.06);
+    --settings-separator-line: var(--cr-separator-line);
 
     --settings-title-bar-background-color: var(--google-blue-700);
     --settings-title-bar-color: rgb(255, 255, 255);
     --settings-title-search-color: rgb(192, 199, 205);
-
-    --settings-actionable: {
-      cursor: pointer;
-    };
   }
 </style>