Change web_tests to work without universal access to file urls

To introduce EventLoop concept we can't have AllowUniversalAccessFromFileURLs changing midway, and so we will be making AllowUniversalAccessFromFileURLs false for web_tests by default.

This CL changes iframes with dataurl to srcdoc since srcdoc allows access without AllowUniversalAccessFromFileURLs.

Change-Id: Ic99ca1aaf33c37365caf7d1218f5847fd36c0409
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1531924
Reviewed-by: Taiju Tsuiki <tzik@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Keishi Hattori <keishi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#652490}