Form validation: Validation bubble should be closed on document unload process.
This CL fixes a bug that a validation bubble is not closed by page navigation in
some cases.
We close a validation message on Page::documentDetached(). However it seems it was
too late to communicate with the browser process in some cases. So, this CL moves
it to Document unload timing.
* Add ValidationMessage::willUnloadDocument(), which closes a validation bubble,
and Document::dispatchUnloadEvents() calls it indirectly through Page.
* HTMLFormControlElement prevents from showing a validation message after the
unload processing.
BUG=704560
Review-Url: https://codereview.chromium.org/2771193002
Cr-Commit-Position: refs/heads/master@{#459701}
8 files changed
