Webkit: add to support file uploading

Summary:
This change adds one function in WebChromeClient for supporting
uploading file in browser. 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.

Test Plan: Needs @randall.rushing branches

Reviewers: randall.rushing

CC: randall.rushing

Differential Revision: http://review.codefirex.com/D388