Split OptionsPage into Page and PageManager.

Split OptionsPage into Page and PageManager.

This is the first step toward consolidating OptionsPage with similar code
in HelpBasePage.

I know this looks huge, but it's mostly renames -- the only changes
that aren't trivial are in:
* c/b/resources/options/options_page.js
* ui/webui/resources/js/cr/ui/page_helper/page.js
* ui/webui/resources/js/cr/ui/page_helper/page_manager.js

==========

This CL moves parts of OptionsPage to the new PageManager and Page objects.
These changes are essentally renames that shouldn't affect functionality.

cr.ui.pageManager.PageManager maintains a list of pages & overlays and can
show and hide overlays, scroll around as needed, etc. Basically what the
OptionsPage "static" members do for overlays.

cr.ui.pageManager.Page is basically the same as the OptionsPage prototype,
the essential attributes of each page/overlay. These will be managed by
the PageManager. Overlays and root pages like BrowserOptions will now descend
from Page.

These may not be the best names, and I don't know if cr.ui as at all the best
place for these classes -- let me know if you object or have better ideas.
Thanks.

==========

Future work:

* Move some logic back to OptionsPage by way of a handler to make
Page and PageManager independent of OptionsPage (e.g., for uber events,
history, and so forth)
* Transition the About page to use Page and PageManager and remove the
old code.
* Separate out bubble logic from general page manipulation.

==========

R=dbeam@chromium.org,stevenjb@chromium.org,

BUG=313244

Review URL: https://codereview.chromium.org/410293004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@286820 0039d316-1c4b-4281-b951-d872f2087c98