Ignore non-focusable field while identifying sections in FormStructure.
This also updates the form data comparison functions which did not include many fields. This manifested as a bug on the 15_crbug_53075 where the shipping field is initially hidden. Because this is hidden, this new code did not compute a section split. When you revealed it, the code did not detect that anything changed and used the cached values computed previously, counting it as no split. Accounting for "focusable" as a change in the form makes this compute properly.
Original patch by ziran.sun@samsung.com https://codereview.chromium.org/
634563002/ This tweaks the test code from Ziran's patch and adds the "heuristics" tests
BUG=231160,426538
Review URL: https://codereview.chromium.org/
678463002
Cr-Commit-Position: refs/heads/master@{#303533}