Migrate FrameHostMsg_DispatchLoad IPC message to Mojo

Add a new method to blink::mojom::LocalFrameHost interface, to be
implemented right from RFHI, which will allow us to remove the
WebLocalFrameClient::DispatchLoad() API plus the related bits
under //content/renderer.

Bug: 1008432
Change-Id: I047cc905c52d9f6a91414190b91c61a83bb48d4b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2000708
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Ken Buchanan <kenrb@chromium.org>
Reviewed-by: Arthur Sonzogni <arthursonzogni@chromium.org>
Reviewed-by: Dave Tapuska <dtapuska@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Mario Sanchez Prada <mario@igalia.com>
Cr-Commit-Position: refs/heads/master@{#733929}
12 files changed