Remove blink::ResourceType::kMainResource

Since we are not loading main resources in blink anymore, we can
get rid of kMainResource type and all the code related to main
resources.

Removing kMainResource from probe::willSendRequest requires splitting
that probe into two: one for subresources, and one for navigation
request. We now pass different parameters to these functions and handle
them separately.

Bug: 855189
Change-Id: I67624e40d9ffddabd685805c0e35acb699685c1c
Reviewed-on: https://chromium-review.googlesource.com/c/1434074
Reviewed-by: Andrey Kosyakov <caseq@chromium.org>
Reviewed-by: Yutaka Hirano <yhirano@chromium.org>
Commit-Queue: Dmitry Gozman <dgozman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#626831}
41 files changed