feat(select): add support for disabled

closes #3518

src/components/select/select-theme.scss

@@ -37,6 +37,9 @@ md-select.md-THEME_NAME-theme {
 }
 
 md-select-menu.md-THEME_NAME-theme {
+  md-option[disabled] {
+    color: '{{foreground-3}}';
+  }
 
   md-optgroup {
     color: '{{foreground-2}}';

src/components/select/select.js

@@ -416,6 +416,10 @@ function SelectMenuDirective($parse, $mdUtil, $mdTheming) {
       var option = $mdUtil.getClosest(ev.target, 'md-option');
       var optionCtrl = option && angular.element(option).data('$mdOptionController');
       if (!option || !optionCtrl) return;
+      if (option.hasAttribute('disabled')) {
+        ev.stopImmediatePropagation();
+        return false;
+      }
 
       var optionHashKey = selectCtrl.hashGetter(optionCtrl.value);
       var isSelected = angular.isDefined(selectCtrl.selected[optionHashKey]);
@@ -645,6 +649,14 @@ function OptionDirective($mdButtonInkRipple, $mdUtil) {
       scope.$watch(function() { return element.text(); }, setOptionValue);
     }
 
+    attr.$observe('disabled', function(disabled) {
+      if (disabled) {
+        element.attr('tabindex', '-1');
+      } else {
+        element.attr('tabindex', '0');
+      }
+    });
+
     scope.$$postDigest(function() {
       attr.$observe('selected', function(selected) {
         if (!angular.isDefined(selected)) return;
@@ -877,16 +889,22 @@ function SelectProvider($$interimElementProvider) {
           var optionsArray = $mdUtil.nodesToArray(optionNodes);
           var index = optionsArray.indexOf(opts.focusedNode);
 
-          if (index === -1) {
-            // We lost the previously focused element, reset to first option
-            index = 0;
-          } else if (direction === 'next' && index < optionsArray.length - 1) {
-            index++;
-          } else if (direction === 'prev' && index > 0) {
-            index--;
-          }
-          var newOption = opts.focusedNode = optionsArray[index];
+          var newOption;
+
+          do {
+            if (index === -1) {
+              // We lost the previously focused element, reset to first option
+              index = 0;
+            } else if (direction === 'next' && index < optionsArray.length - 1) {
+              index++;
+            } else if (direction === 'prev' && index > 0) {
+              index--;
+            }
+            newOption = optionsArray[index];
+            if (newOption.hasAttribute('disabled')) newOption = undefined;
+          } while (!newOption && index < optionsArray.length - 1 && index > 0)
           newOption && newOption.focus();
+          opts.focusedNode = newOption;
         }
         function focusNextOption() {
           focusOption('next');
@@ -1069,7 +1087,7 @@ function SelectProvider($$interimElementProvider) {
       $$rAF(function() {
         element.addClass('md-active');
         selectNode.style[$mdConstant.CSS.TRANSFORM] = '';
-        if (focusedNode) {
+        if (focusedNode && !focusedNode.hasAttribute('disabled')) {
           opts.focusedNode = focusedNode;
           focusedNode.focus();
         }