Update android generator to handle java7.

This is a combination of several commits made
to these files:

https://chromiumcodereview.appspot.com/23587011
https://codereview.chromium.org/23702057
https://codereview.chromium.org/40523002
https://codereview.chromium.org/49913003

Change-Id: Id944decfde8590c3a6e548ac66f598c45de7169e
android_webview: add to support file uploading

This commit changes function from empty implementation
to abstract function interface in AwContentsClient for
supporting uploading file in browser. Its subclass will
override this function. In Android 4.4, browser is based
on chromium not webkit engine, chromium engine support
uploading file and will callback to client to show file
chooser, but android_webview client has empty
implementation within this callback for file chooser.

So we solve this issue by adding implementation in framework
chromium client which extends android_webview client, function
in framework webkit client and corresponding functions in
browser app.

Change-Id: I50375573848879f3c30069b1831b314f0c536163