fix(chips): do not trim the input model.

* The chips input should not trim the text, because otherwise the buffer will be always falsey, even when there are spaces in the input, and this would cause the backspace not to work.

Fixes angular#7243

src/components/chips/chips.spec.js

@@ -388,8 +388,37 @@ describe('<md-chips>', function() {
           expect(enterEvent.preventDefault).toHaveBeenCalled();
         }));
 
+        it('should not trim the input text', inject(function($mdConstant) {
+          var element = buildChips(BASIC_CHIP_TEMPLATE);
+          var ctrl = element.controller('mdChips');
+          var input = element.find('input');
+
+          input.val('    ');
+          input.triggerHandler('input');
+
+          expect(ctrl.chipBuffer).toBeTruthy();
+
+          var enterEvent = {
+            type: 'keydown',
+            keyCode: $mdConstant.KEY_CODE.BACKSPACE,
+            which: $mdConstant.KEY_CODE.BACKSPACE,
+            preventDefault: jasmine.createSpy('preventDefault')
+          };
+
+          input.triggerHandler(enterEvent);
+
+          expect(enterEvent.preventDefault).not.toHaveBeenCalled();
+
+          input.val('');
+          input.triggerHandler('input');
+
+          input.triggerHandler(enterEvent);
+
+          expect(enterEvent.preventDefault).toHaveBeenCalledTimes(1);
+        }));
       });
 
+
       it('focuses/blurs the component when focusing/blurring the input', inject(function() {
         var element = buildChips(BASIC_CHIP_TEMPLATE);
         var ctrl = element.controller('mdChips');

src/components/chips/js/chipsDirective.js

@@ -154,6 +154,7 @@
             ng-model="$mdChipsCtrl.chipBuffer"\
             ng-focus="$mdChipsCtrl.onInputFocus()"\
             ng-blur="$mdChipsCtrl.onInputBlur()"\
+            ng-trim="false"\
             ng-keydown="$mdChipsCtrl.inputKeydown($event)">';
 
   var CHIP_DEFAULT_TEMPLATE = '\