Identity API: Change WebAuthFlow to use <webview> instead of a normal browser pop-up.

Identity API: Change WebAuthFlow to use <webview> instead of a normal browser pop-up.

All Identity API UI is moving into a webview tag inside a component app, allowing Chrome Apps
to be isolated from the browser.

The launchWebAuthFlow API is affected by this change. The getAuthToken API will be updated
to use WebAuthFlow instead of native dialogs in a separate change.

The WebAuthFlow unit tests have been deleted. They weren't providing anything that isn't
covered in the browser tests for launchWebAuthFlow.

Two features of the (experimental) API have been removed. The chrome-extension: is not supported
in webviews. HTTPS must be used instead. Explicit control over the size of the dialog is no
longer supported.

BUG=228908
(This is step #6 in the description.)

[Michael Courage, 2013-04-22 20:27:14]

LaunchWebAuthFlow opens up a browser window to navigate through authentication
and authorization flows with arbitrary web identity providers.

This change adds a component app to display the flow, replacing the browser
pop-up that was used previously. Aside from a couple of small exceptions noted
in the description, the API itself is unchanged.

This change depends on https://codereview.chromium.org/14122025/, which adds
some PNGs used in the component app.

OWNERS file division:
miket: chrome/*/extensions/*
jhawkins: chrome/browser/resources/identity_api_ui/*

Mike, you'll probably have to look at everything since the component app
behavior is coupled pretty tightly with the WebAuthFlow class.

[Michael Courage, 2013-05-07 00:12:04]

PTAL. This patch no longer changes the behavior of chrome.experimental.identity.

There are a couple of other changes if you happen to have read the first
patchset. The standard dialog box images are now used in the component app, the
token cache was merged in from a previous commit.

[James Hawkins, 2013-05-07 17:43:31]

This CL is huge; can you break it up (I'm pretty sure you can)?

[Michael Courage, 2013-05-07 17:50:10]

On 2013/05/07 17:43:31, James Hawkins wrote:
> This CL is huge; can you break it up (I'm pretty sure you can)?

I'll see what I can do. It's actually already the result of splitting up a much
larger change, but I may be able to factor out a little more.

[James Hawkins, 2013-05-07 17:53:24]

On 2013/05/07 17:50:10, Michael Courage wrote:
> On 2013/05/07 17:43:31, James Hawkins wrote:
> > This CL is huge; can you break it up (I'm pretty sure you can)?
> 
> I'll see what I can do. It's actually already the result of splitting up a
much
> larger change, but I may be able to factor out a little more.

The added files can be done in chunks (though I think you'll need to pull in
other reviewers, e.g. extensions, for some of them).