Bug 1426979 P1 Ignore about:blank and about:srcdoc channels when determining if a window ClientSource is controlled or not. r=asuth

dom/base/nsGlobalWindowInner.cpp

@@ -1750,8 +1750,32 @@ nsGlobalWindowInner::EnsureClientSource()
 
   bool newClientSource = false;
 
+  // Get the load info for the document if we performed a load.  Be careful
+  // not to look at about:blank or about:srcdoc loads, though. They will have
+  // a channel and loadinfo, but their loadinfo will never be controlled.  This
+  // would in turn inadvertantly trigger the logic below to clear the inherited
+  // controller.
+  nsCOMPtr<nsILoadInfo> loadInfo;
   nsCOMPtr<nsIChannel> channel = mDoc->GetChannel();
-  nsCOMPtr<nsILoadInfo> loadInfo = channel ? channel->GetLoadInfo() : nullptr;
+  if (channel) {
+    nsCOMPtr<nsIURI> uri;
+    Unused << channel->GetURI(getter_AddRefs(uri));
+
+    bool ignoreLoadInfo = false;
+
+    // Note, this is mostly copied from NS_IsAboutBlank().  Its duplicated
+    // here so we can efficiently check about:srcdoc as well.
+    bool isAbout = false;
+    if (NS_SUCCEEDED(uri->SchemeIs("about", &isAbout)) && isAbout) {
+      nsCString spec = uri->GetSpecOrDefault();
+      ignoreLoadInfo = spec.EqualsLiteral("about:blank") ||
+                       spec.EqualsLiteral("about:srcdoc");
+    }
+
+    if (!ignoreLoadInfo) {
+      loadInfo = channel->GetLoadInfo();
+    }
+  }
 
   // Take the initial client source from the docshell immediately.  Even if we
   // don't end up using it here we should consume it.