Make html metadata follow the spec.

tools/dom/templates/html/impl/impl_HTMLInputElement.darttemplate

Index: tools/dom/templates/html/impl/impl_HTMLInputElement.darttemplate
diff --git a/tools/dom/templates/html/impl/impl_HTMLInputElement.darttemplate b/tools/dom/templates/html/impl/impl_HTMLInputElement.darttemplate
index 0a75f744f1b4a53e99d7f9ed50b04fdd0240d98a..2aa82b036c598735d277ed2a9573d925263822fb 100644
--- a/tools/dom/templates/html/impl/impl_HTMLInputElement.darttemplate
+++ b/tools/dom/templates/html/impl/impl_HTMLInputElement.darttemplate
@@ -308,7 +308,7 @@ abstract class RangeInputElementBase implements InputElementBase {
  * Use [supported] to check if this is supported on the current platform.
  */
 @SupportedBrowser(SupportedBrowser.CHROME, '25')
-@Experimental
+@Experimental()
 abstract class DateInputElement implements RangeInputElementBase {
   factory DateInputElement() => new InputElement(type: 'date');
 
@@ -333,7 +333,7 @@ abstract class DateInputElement implements RangeInputElementBase {
  * Use [supported] to check if this is supported on the current platform.
  */
 @SupportedBrowser(SupportedBrowser.CHROME, '25')
-@Experimental
+@Experimental()
 abstract class MonthInputElement implements RangeInputElementBase {
   factory MonthInputElement() => new InputElement(type: 'month');
 
@@ -358,7 +358,7 @@ abstract class MonthInputElement implements RangeInputElementBase {
  * Use [supported] to check if this is supported on the current platform.
  */
 @SupportedBrowser(SupportedBrowser.CHROME, '25')
-@Experimental
+@Experimental()
 abstract class WeekInputElement implements RangeInputElementBase {
   factory WeekInputElement() => new InputElement(type: 'week');
 
@@ -383,7 +383,7 @@ abstract class WeekInputElement implements RangeInputElementBase {
  * Use [supported] to check if this is supported on the current platform.
  */
 @SupportedBrowser(SupportedBrowser.CHROME)
-@Experimental
+@Experimental()
 abstract class TimeInputElement implements RangeInputElementBase {
   factory TimeInputElement() => new InputElement(type: 'time');
 
@@ -409,7 +409,7 @@ abstract class TimeInputElement implements RangeInputElementBase {
  * Use [supported] to check if this is supported on the current platform.
  */
 @SupportedBrowser(SupportedBrowser.CHROME, '25')
-@Experimental
+@Experimental()
 abstract class LocalDateTimeInputElement implements RangeInputElementBase {
   factory LocalDateTimeInputElement() =>
       new InputElement(type: 'datetime-local');
@@ -432,7 +432,7 @@ abstract class LocalDateTimeInputElement implements RangeInputElementBase {
 @SupportedBrowser(SupportedBrowser.CHROME)
 @SupportedBrowser(SupportedBrowser.IE)
 @SupportedBrowser(SupportedBrowser.SAFARI)
-@Experimental
+@Experimental()
 abstract class NumberInputElement implements RangeInputElementBase {
   factory NumberInputElement() => new InputElement(type: 'number');
 
@@ -459,7 +459,7 @@ abstract class NumberInputElement implements RangeInputElementBase {
  */
 @SupportedBrowser(SupportedBrowser.CHROME)
 @SupportedBrowser(SupportedBrowser.IE, '10')
-@Experimental
+@Experimental()
 abstract class RangeInputElement implements RangeInputElementBase {
   factory RangeInputElement() => new InputElement(type: 'range');