Add --expose-internals-for-testing flag

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 78eb53aa273ef7ee8f760c17384df3fe09e020b3..b4184a7d25113b0aead664b0056de6439e6bcc63 100644
--- a/content/public/common/content_switches.cc
+++ b/content/public/common/content_switches.cc
@@ -468,6 +468,11 @@ const char kEnableViewport[]                = "enable-viewport";
 // - Location platform support for Windows 7
 const char kExperimentalLocationFeatures[]  = "experimental-location-features";
 
+// Exposes the window.internals object to JavaScript for interactive development
+// and debugging of layout tests that rely on it.  For testing only, since
+// (like other testing flags) it has security implications.
+const char kExposeInternalsForTesting[]     = "expose-internals-for-testing";
+
 // If accelerated compositing is supported, always enter compositing mode for
 // the base layer even when compositing is not strictly required.
 const char kForceCompositingMode[]          = "force-compositing-mode";