Refactor ResourceFetcher factory functions in FrameFetchContext

 - FrameFetchContext::CreateFetcherFromDocument sounds too generic. It's
   for HTML imports, so rename it to
   FrameFetchContext::CreateFetcherForImportedDocument.
 - Rename FrameFetchContext::CreateFetcherFromDocumentLoader to
   FrameFetchContext::CreateFetcher because it is the default path.
 - FrameFetchContext::FrameFetchContext(DocumentLoader*, Document*)
   expects exactly one of its two arguments is non-null. Split it to
   two for readability.

Bug: 914739
Change-Id: I50343f067d1b7687849ea348fadcd365567fcd6a
Reviewed-on: https://chromium-review.googlesource.com/c/1388354
Commit-Queue: Yutaka Hirano <yhirano@chromium.org>
Reviewed-by: Hiroshige Hayashizaki <hiroshige@chromium.org>
Reviewed-by: Hiroki Nakagawa <nhiroki@chromium.org>
Cr-Commit-Position: refs/heads/master@{#619000}
4 files changed