Port messages sent by WebIDBCursorImpl to Mojo.

This is the third and final patch in a series that converts the IPC
messages sent by WebIDBFactoryImpl, WebIDBDatabaseImpl and
WebIDBCursorImpl to Mojo messages.

This is a mostly mechanical change which also allows a lot of code
supporting the legacy IPC messages to be removed.

BUG=627484

Review-Url: https://codereview.chromium.org/2500263003
Cr-Commit-Position: refs/heads/master@{#433964}
31 files changed