Drop malformed url requests for non-main frame (was: AmazonWebView does not have WebResourceRequest)

[ekager]

shouldInterceptRequest method takes a string instead of WebResourceRequest with AmazonWebView. Look into if we need to create a WebResourceRequest here.

[ekager]

I don't think it's possible to create a WebResourceRequest object from the string. We may be able to salvage some of the code because the String "request" is the URL of the request and a lot of the code in Focus is about matching the URLs to know which URL to show in the URL bar.

[mcomella]

The only method we use is request.isForMainFrame, which I think we can check with the TrackingProtectionWebViewClient.currentPageUrl:

        if (!request.isForMainFrame() &&
                !scheme.equals("http") && !scheme.equals("https")) {
            // Block any malformed non-http(s) URIs. WebView will already ignore things like market: URLs,
            // but not in all cases (malformed market: URIs, such as market:://... will still end up here).
            // (Note: data: URIs are automatically handled by WebView, and won't end up here either.)
            // file:// URIs are disabled separately by setting WebSettings.setAllowFileAccess()
            return new AmazonWebResourceResponse(null, null, null);
        }

I didn't have time to investigate whether or not this would be sufficient, however.

Note that the UrlMatcher for tracking protection whitelists first-party requests (against the currentPageUrl so the later code that checks against for main frames is actually unnecessary, afaict. I removed it in #311.

[mcomella]

liuche found where this was initially implemented and it contains useful comments: mozilla-mobile/focus-android#106 (comment)

[mcomella]

[triage] We're going to wait on the WebView upgrade to see if this API is added back in #379.

[mcomella]

This is handled by components now: they're probably doing the right thing. :)