Which test shell, android_webview_apk or system_webview_shell_apk?

Either one, it's not too hard to implement onShowCustomView and onHideCustomView. Just copy the implementation from the test should be fine.

system webview shell would be best for us I believe. (I think the easiest workflow for us non-webview people is to build system_webview_apk with  system_webview_shell_package_name="com.google.android.webview")

Looking at the code today, I think arbitrary element full screen *is* supported in webview. It's just neither test shells implement the webview callbacks required for full screen.

So just need to verify this is the case.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/6a321a7e3cfe5b7272da3c0f99cf200ee09927fd

commit 6a321a7e3cfe5b7272da3c0f99cf200ee09927fd
Author: tobiasjs <tobiasjs@chromium.org>
Date: Thu May 19 11:04:09 2016

Support fullscreen in webview shell.

BUG= 612587 

Review-Url: https://codereview.chromium.org/1990743003
Cr-Commit-Position: refs/heads/master@{#394731}

[modify] https://crrev.com/6a321a7e3cfe5b7272da3c0f99cf200ee09927fd/android_webview/tools/system_webview_shell/apk/src/org/chromium/webview_shell/WebViewBrowserActivity.java

SystemWebviewShell.apk should support fullscreen now. watk@ - is this sufficient for your needs?

Awesome! Just tried it and it works.