Fix WebChromeClientTest#testOnJsBeforeUnload

Chromium has removed the ability of webpages to specify strings for the
onbeforeunload dialog.  So don't verify the unload message. Just make sure the
WebChromeClient callback is fired.

Also changed the test name to testOnJsBeforeUnloadIsCalled.

BUG:27745434
Change-Id: If2d56375a2941c004bad3c713f747093fc09ca79
2 files changed