fix(input): use ValidityState to determine validity

In browsers where HTML5 constraint validation is (partially) implemented, an invalid number
entered into an input[type=number] (for example) input element would be visible to the
script context as the empty string. When the required or ngRequired attributes are not used,
this results in the invalid state of the input being ignored and considered valid.

To address this, a validator which considers the state of the HTML5 ValidityState object is
used when available.

Closes angular#4293
Closes angular#2144
Closes angular#4857
Closes angular#5120
Closes angular#4945
Closes angular#5500

src/ng/directive/input.js

@@ -404,7 +404,28 @@ function validate(ctrl, validatorName, validity, value){
   return validity ? value : undefined;
 }
 
+
+function validateHtml5(ctrl, validatorName, element) {
+  var v = element.prop('validity');
+  if (v && isObject(v)) {
+    var validator = function(value) {
+      // Don't overwrite previous validation, don't consider valueMissing to apply (ng-required can
+      // perform the required validation)
+      if (!ctrl.$error[validatorName] && (v.badInput || v.customError || v.typeMismatch) &&
+          !v.valueMissing) {
+        ctrl.$setValidity(validatorName, false);
+        return undefined;
+      }
+      return value;
+    };
+    ctrl.$parsers.push(validator);
+    ctrl.$formatters.push(validator);
+  }
+}
+
 function textInputType(scope, element, attr, ctrl, $sniffer, $browser) {
+  var validity = element.prop('validity');
+  validity = isObject(validity) && validity;
   // In composition mode, users are still inputing intermediate text buffer,
   // hold the listener until composition is done.
   // More about composition events: https://developer.mozilla.org/en-US/docs/Web/API/CompositionEvent
@@ -431,7 +452,7 @@ function textInputType(scope, element, attr, ctrl, $sniffer, $browser) {
       value = trim(value);
     }
 
-    if (ctrl.$viewValue !== value) {
+    if (ctrl.$viewValue !== value || (validity && !value && !validity.valueMissing)) {
       if (scope.$$phase) {
         ctrl.$setViewValue(value);
       } else {
@@ -551,6 +572,8 @@ function numberInputType(scope, element, attr, ctrl, $sniffer, $browser) {
     }
   });
 
+  validateHtml5(ctrl, 'number', element);
+
   ctrl.$formatters.push(function(value) {
     return ctrl.$isEmpty(value) ? '' : '' + value;
   });