Revert of Remove about:srcdoc url conversion.

content/browser/renderer_host/render_process_host_impl.cc

Index: content/browser/renderer_host/render_process_host_impl.cc
diff --git a/content/browser/renderer_host/render_process_host_impl.cc b/content/browser/renderer_host/render_process_host_impl.cc
index a9be00c263d13664681b4cfde2d9f6fe7aa93919..597e977a184e46bb5ce9597fa8a5e3160a2c6c61 100644
--- a/content/browser/renderer_host/render_process_host_impl.cc
+++ b/content/browser/renderer_host/render_process_host_impl.cc
@@ -2369,6 +2369,12 @@
     return;
   }
 
+  if (url->SchemeIs(url::kAboutScheme)) {
+    // The renderer treats all URLs in the about: scheme as being about:blank.
+    // Canonicalize about: URLs to about:blank.
+    *url = GURL(url::kAboutBlankURL);
+  }
+
   if (!policy->CanRequestURL(rph->GetID(), *url)) {
     // If this renderer is not permitted to request this URL, we invalidate the
     // URL.  This prevents us from storing the blocked URL and becoming confused