Revert 115549 - Ensure that there's always a provisional document loader if the frame loader is in …

Revert 115549 - Ensure that there's always a provisional document loader if the frame loader is in provisional state
https://bugs.webkit.org/show_bug.cgi?id=83894

Reviewed by Nate Chapin.

We're still seeing crashes in the FrameLoader where the FrameLoader's
state is "provisional" but there is no provisional document loader. I
added code to update the FrameLoader's state everytime the provisional
document loader is cleared, and added checks that the FrameLoader's
state can't be set to provisional without a provisional loader.

If the crashes go away, or the newly added checks reveal the culprit,
we should relex the checks to use ASSERT() instead of CRASH().

* loader/FrameLoader.cpp:
(WebCore::FrameLoader::init):
(WebCore::FrameLoader::setupForReplace):
(WebCore::FrameLoader::stopAllLoaders):
(WebCore::FrameLoader::clearProvisionalLoad):
(WebCore::FrameLoader::continueFragmentScrollAfterNavigationPolicy):
(WebCore::FrameLoader::continueLoadAfterNavigationPolicy):


TBR=jochen@chromium.org
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=115916