Cached files are requested again from web server (JNLP applet)

HTTP HEADER "Expires" is honored by plug-in.

Steps to reproduce:
1. Download tomcat from http://stt-13.ru.oracle.com/newroot/testsuites/180_user_ws/stden/tomcat/tomcat-JDK-8056933.zip
2. Unpack and run it (Catalina run).
3. Open Java Control Panel / Security tab, click "Edit Site List...", add "http://127.0.0.1:8080" to ESL List. Go to Advanced, set Enable tracing + logging + Show applet livecycle exceptions + Show console.
2. Clear cache.
3. Load the applet page which requests to download a jar: http://127.0.0.1:8080/HTTP_Header/html/testRunBeforeExpireNoUpdateJnlp.html
4. The web server will return the jar back with HTTP HEADER "Expires" with date in the future.
5. Close the applet page and then make sure the jar is cached.
6. Load the applet page at step #1 again.
7. The cache will NOT try to get the jar again back from the web server because the cache is NOT expired.

Bug is reproduced if the second launch trigger a new request to the web server.

Tests failed 7u80 b02: http://aurora-ds3.us.oracle.com:9502/runs/574768.STT-DEPLOYMENT-1/reports/html/all-tests.html

HTTP_HeaderTest::testRunBeforeExpireNoUpdateJnlp
Cache verification failed. Reason: Expect no http request/response at all. But got: Entries size: 1 Entry[0]: requestUrl: http://127.0.0.1:8080/HTTP_Header_Filter/classes/RunBeforeExpireNoUpdateJnlp.jar responseCode: 304

HTTP_HeaderTest::testRunBeforeExpireWithUpdateJnlp
Cache verification failed. Reason: Expect no http request/reponse at all. But got: Entries size: 2 Entry[0]: requestUrl: http://127.0.0.1:8080/HTTP_Header_Filter/classes/RunBeforeExpireWithUpdateJnlp.jar responseCode: 200 Entry[1]: requestUrl: http://127.0.0.1:8080/HTTP_Header_Filter/classes/RunBeforeExpireWithUpdateJnlp.jar responseCode: 200

RULE HTTP_HeaderTest::testRunBeforeExpireNoUpdateJnlp any any
RULE HTTP_HeaderTest::testRunBeforeExpireWithUpdateJnlp any any