Fix #9685 Date is not a content header (#9687)

resetContent does not reset Date Header

Signed-off-by: gregw <gregw@webtide.com>

jetty-server/src/main/java/org/eclipse/jetty/server/Response.java

@@ -1253,7 +1253,6 @@ public class Response implements HttpServletResponse
                 case LAST_MODIFIED:
                 case EXPIRES:
                 case ETAG:
-                case DATE:
                 case VARY:
                     i.remove();
                     continue;

jetty-server/src/test/java/org/eclipse/jetty/server/ErrorHandlerTest.java

@@ -154,6 +154,7 @@ public class ErrorHandlerTest
         assertThat("Response status code", response.getStatus(), is(404));
         assertThat("Response Content-Length", response.getField(HttpHeader.CONTENT_LENGTH).getIntValue(), greaterThan(0));
         assertThat("Response Content-Type", response.get(HttpHeader.CONTENT_TYPE), containsString("text/html;charset=ISO-8859-1"));
+        assertThat(response.get(HttpHeader.DATE), notNullValue());
         assertThat(response.getContent(), containsString("content=\"text/html;charset=ISO-8859-1\""));
 
         assertContent(response);

jetty-server/src/test/java/org/eclipse/jetty/server/ResponseTest.java

@@ -2090,6 +2090,7 @@ public class ResponseTest
         response.setContentType("some/type");
         response.setContentLength(3);
         response.setHeader(HttpHeader.EXPIRES, "never");
+        response.setHeader(HttpHeader.DATE, "2000-01-01");
 
         response.setHeader("SomeHeader", "SomeValue");
 
@@ -2106,6 +2107,7 @@ public class ResponseTest
 
         // check arbitrary header still set
         assertThat(response.getHeader("SomeHeader"), is("SomeValue"));
+        assertThat(response.getHeader("Date"), is("2000-01-01"));
 
         // check cookies are still there
         Enumeration<String> set = response.getHttpFields().getValues("Set-Cookie");