[Android] Fix XWalkCoreInternalTest failure

Including:
ExtensionBroadcastInternalTest#test
ExtensionEchoInternalTest#testMultiFrames
WebNotificationTest#testWebNotificationShowAndCloseByUser
WebNotificationTest#testWebNotificationShowAndCloseByJs

For WebNotification, it's missing handling of empty icon.
For Extension, it's using both sync load and title listener,
use async load instead.

BUG=https://crosswalk-project.org/jira/browse/XWALK-3215
Merge pull request #2752 from wang16/core_internal_test

[Android] Fix XWalkCoreInternalTest failure