GitLab

Exposed a function BrowserViewRenderer::FromWebContents to allow
android_webview/browser/ layer to get hold of the instance of
BrowserViewRenderer through WebContents, without the help of AwContents,
which is in android_webview/native/ layer.

BUG=459779, 460826

Review URL: https://codereview.chromium.org/950973003

Cr-Commit-Position: refs/heads/master@{#318264}