Add new snackbar features to prepare for omnibox geolocation snackbar.

Add new snackbar features to prepare for omnibox geolocation snackbar.

This adds a few new features to snackbars to prepare for the geolocation
disclosure snackbar:
 - Snackbars now interact nicely with the keyboard. Snackbars won't
   overlap the keyboard; instead, they're appear above the keyboard if
   the keyboard is showing, and will drop down the bottom of the screen
   when the keyboard is hidden. This is achieved using
   View.getWindowVisibleDisplayFrame() to find where the keyboard is
   showing.
 - Snackbars now support multiline text. In this case, the snackbar text
   won't be ellipsized and TemplatePreservingTextView will act like a
   normal TextView.
 - Snackbar text can now be any CharSequence, not just a String. This
   will be used to display snackbars that contain spans.

Implementation change: this adds a Snackbar class, which allows greater
flexibility when configuring snackbars. SnackbarManager.showSnackbar()
now acceps a single Snackbar, instead of a long list of parameters.

BUG=505481

Review URL: https://codereview.chromium.org/1229733002

Cr-Commit-Position: refs/heads/master@{#337966}