Use default CSP for resource loading in webview (instead of platform app's CSP)
<webview> loads page in an isolated context inside platform app and hosts drive-by web. Platform app's CSP is too restrictive for <webview>, we stop using that CSP and use the default instead in this CL.
BUG=
363437
Test=Load an chrome app. Load a webview html from accessible resources. Make the webview page contain inline JS. Check that the JS loads. It didn't use to load w/o this CL.
Committed:
https://src.chromium.org/viewvc/chrome?view=rev&revision=264253