[Offline pages] Downloads UI: Adding bridge for issuing notifications
Changes:
* Updates DownloadNotifiactionSerivce to include handling of offline pages
* Adds openItem and destroy methods to DownloadServiceDelegate (to handle offline pages and prevent memory leaks)
* Adds notification bridge for offline pages related downloads (implemented on C++ and Java side) only calls from c++ to Java.
* Adds interface to components that will be implemented by the bridge
* Updating OPDownloadBridge to issue notification when current page is captured.
* Adding copy constructor to DownloadUIItem
BUG=
630817
Committed:
https://crrev.com/9e8c5f4e30270447969f04bfe4d676b6d94f25b9
Cr-Commit-Position: refs/heads/master@{#413214}