[test] Run Devtools frontend at different site from inspected page

Currently, devtools web tests serve devtools and the inspected page
from the same site. This interferes with the ongoing experiments
that put the same-site tabs in the same process.

This patch makes sure we serve devtools from a different site from
the inspected page. This is more in line with how we run devtools
in production.

Bug: chromium:1444827
Change-Id: I144f6844fcafe496483ac2e3482a789c37b8856a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4574441
Reviewed-by: Avi Drissman <avi@chromium.org>
Reviewed-by: Simon Zünd <szuend@chromium.org>
Commit-Queue: Jaroslav Sevcik <jarin@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1151681}

content/web_test/browser/web_test_devtools_bindings.cc

@@ -25,9 +25,12 @@
 
 namespace {
 
+const char kDevToolsFrontendOrigin[] = "debug-frontend.test";
+const char kOriginToReplace[] = "127.0.0.1";
+
 GURL GetInspectedPageURL(const GURL& test_url) {
   std::string spec = test_url.spec();
-  std::string test_query_param = "&test=";
+  std::string test_query_param = "&inspected_test=";
   std::string test_script_url =
       spec.substr(spec.find(test_query_param) + test_query_param.length());
   std::string inspected_page_url = test_script_url.replace(
@@ -86,11 +89,20 @@ GURL WebTestDevToolsBindings::MapTestURLIfNeeded(const GURL& test_url,
   // To reduce timeouts, we need to load DevTools resources from the same
   // origin as the `test_url_string`.
   CHECK_NE(test_url_string.find("127.0.0.1:8000"), std::string::npos);
-  std::string url_string = "http://127.0.0.1:8000/inspector-sources/";
+  std::string url_string = "http://" + std::string(kDevToolsFrontendOrigin) +
+                           ":8000/inspector-sources/";
   url_string += "integration_test_runner.html?experiments=true";
   if (is_debug_dev_tools)
     url_string += "&debugFrontend=true";
-  url_string += "&test=" + test_url_string;
+
+  std::string devtools_test_url = test_url_string;
+  devtools_test_url.replace(test_url_string.find(kOriginToReplace),
+                            std::strlen(kOriginToReplace),
+                            kDevToolsFrontendOrigin);
+
+  url_string += "&test=" + devtools_test_url;
+  url_string += "&inspected_test=" + test_url_string;
+
 #if !BUILDFLAG(IS_ANDROID) && !BUILDFLAG(IS_IOS)
   if (base::CommandLine::ForCurrentProcess()->HasSwitch(
           switches::kContentShellDevToolsTabTarget)) {