Add screenshot to Assistant feedback UI

1. Moved code to send Assistant feedback from feedback_private_api.cc to
feedback_service.cc as we need to send screenshot.
2. Update one more parameter to SendAssistantFeedback in assistant controller
to send screenshot.

Bug: b/123422976
Change-Id: I7a0e812a994803fbd05b66beed4dfbd29181ed8c
Reviewed-on: https://chromium-review.googlesource.com/c/1441112
Commit-Queue: Xiao Yang <[email protected]>
Reviewed-by: Xiaohui Chen <[email protected]>
Reviewed-by: Dominick Ng <[email protected]>
Reviewed-by: Ahmed Fakhry <[email protected]>
Cr-Commit-Position: refs/heads/master@{#628606}
9 files changed