GitLab

- Adds a CastWebContents::FromWebContents() method to retrieve
corresponding CastWebContents that wrapped the content::CastWebContents.
- Adds flags into CastWebContents::InitParams to determine whether
enabling WebSQL database and mixer audio.

Merge-With: eureka-internal/342751

Bug: internal b/144316145
Test: CQ
Change-Id: I7768e9b2d903ea79dbb3e49ca82ffe389f98d19e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1954447Reviewed-by: Sean Topping <seantopping@chromium.org>
Reviewed-by: Yuchen Liu <yucliu@chromium.org>
Commit-Queue: Jiawei Li <lijiawei@chromium.org>
Cr-Commit-Position: refs/heads/master@{#722614}