Correctly update frame load type after same-doc (history) navigation completion

For same document navigation the |FrameLoader::m_loadType| is set temporarily which means it gets
reset once load completes. This ensures we do not incorrectly attempt to restore scroll position
on content/frame size change once navigation is finished.

BUG=574487
TEST=fast/loader/scroll-restore-should-happen-during-load.html

Review URL: https://codereview.chromium.org/1561573004

Cr-Commit-Position: refs/heads/master@{#369169}
4 files changed