Fix CTS android.webkit package testAccessCacheMode seldom fail issue

Seldom fail below 20%,Since there is no PollingCheck() called right after 
loadAssetUrl() (line 212), the FAV_ICON server request could be sent after the
 cache mode is set to LOAD_NO_CACHE. So there could be one excess server request count of FAV_ICON during the third and the fourth loadAssetUrl()
 request.

The variable "thirdFetch" value is expected to be:
The first loadAssetUrl() request and first FAV_ICON request in LOAD_CACHE_ELSE_NETWORK cache mode + The third loadAssetUrl() request and the 
third FAV_ICON request in  LOAD_NO_CACHE cache mode + The fourth loadAssetUrl()
 request and the fourth FAV_ICON request in LOAD_NO_CACHE cache mode.That is 6.

But the mWebServer.getRequestCount() value could be 7 if the CTS server has
 received the last FAV_ICON request before the cache mode is set to
 LOAD_CACHE_ONLY.

We have reproduced in Nexus with Android 4.4.2

Change-Id: I4a75e8a8fb1ced884cb0785b4891bf99a29c186e
Signed-off-by: Junjie Hu <junjie.hu@mediatek.com>