fix(input): IE perf with attribute selectors for ngMessages

IE manifest huge performance issues with attribute selectors.
Reproduce this very easily using `UI Responsivess` tab in IE11 developer tools:

*  duplicate the amount of ` :not` selectors prefixed with space and
*  measure the time it takes for IE to calculate layout(in green).

Closes #7360

Author: Nissan Hanina

src/components/input/demoErrors/index.html

@@ -59,7 +59,7 @@
         </div>
       </md-input-container>
 
-      <p>
+      <p style="font-size:.8em; width: 100%; text-align: center;">
         Make sure to include <a href="https://docs.angularjs.org/api/ngMessages" target="_blank">ngMessages</a> module when using ng-message markup.
       </p>
     </form>

src/components/input/input-theme.scss

@@ -28,8 +28,9 @@ md-input-container.md-THEME_NAME-theme {
   ng-message, data-ng-message, x-ng-message,
   [ng-message], [data-ng-message], [x-ng-message],
   [ng-message-exp], [data-ng-message-exp], [x-ng-message-exp] {
-    :not(.md-char-counter) {
-      color: '{{warn-A700}}';
+    color: '{{warn-A700}}';
+    .md-char-counter {
+      color: '{{foreground-1}}';
     }
   }