[FastTextAutosizer] Refactor for understandability

This patch is a followup to [1] to cleanup the dependencies on
the old text autosizer. The largest change in this patch is to
remove the "container" concept and rely only on clusters and
blocks in the FastTextAutosizer.

The big changes in this patch include:
* formInputTags vector -> isFormInput(const Element*)
    Passing around a static vector was unnecessarily confusing. This
    patch refactors the formInput statics into a single function:
    isFormInput.
* isAutosizingContainer -> !isExemptFromAutosizer
    The logic of isAutosizingContainer has been switched in
    isExemptFromAutosizer and I think the new name better reflects
    what this function does.
* containerIsRowOfLinks -> blockContainsRowOfLinks
* contentHeightIsConstrained -> blockHeightConstrained
* containerContainsOneOfTags -> blockContainsFormInput
* containerShouldBeAutosized -> !blockPreventedFromAutosizing
    The logic of containerShouldBeAutosized has been switched in
    blockPreventedFromAutosizing. I think this better reflects what
    this function does.
* blockMightBecomeAutosizingCluster has been added.
* isFingerprintingCandidate has been removed in favor of
    blockMightBecomeAutosizingCluster

[1] https://codereview.chromium.org/200603002

BUG=302005

Review URL: https://codereview.chromium.org/197883013

git-svn-id: svn://svn.chromium.org/blink/trunk@169511 bbb929c8-8fbe-4397-9dbb-9b2b20218538