[content shell] allow universal access from file URLs in layout tests

content/public/common/content_switches.cc

Index: content/public/common/content_switches.cc
diff --git a/content/public/common/content_switches.cc b/content/public/common/content_switches.cc
index 2cb2ec7a1a036ae807ab7893735b79ac87e08a71..047c8e9bc24545c04239498cdc61d2310df965f8 100644
--- a/content/public/common/content_switches.cc
+++ b/content/public/common/content_switches.cc
@@ -10,6 +10,11 @@ namespace switches {
 // override for developers who need the old behavior for testing.
 const char kAllowFileAccessFromFiles[]      = "allow-file-access-from-files";
 
+// Explicitely grant the ability to access every other SecurityOrigin to
+// file URLs. This is a security havoc and should only be used for testing.
+const char kAllowUniversalAccessFromFiles[] =
+    "allow-universal-access-from-files";
+
 // Allows debugging of sandboxed processes (see zygote_main_linux.cc).
 const char kAllowSandboxDebugging[]         = "allow-sandbox-debugging";