Add a switch to invert web contents (non-accel only).

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 6baf3c79e6ae3d003c0218939aaac9a643a4e1d5..0bec7fa0754bb1814fc0bb1910992e954bc1584b 100644
--- a/content/public/common/content_switches.cc
+++ b/content/public/common/content_switches.cc
@@ -373,6 +373,10 @@ const char kInProcessPlugins[]              = "in-process-plugins";
 // Runs WebGL inside the renderer process.
 const char kInProcessWebGL[]                = "in-process-webgl";
 
+// Invert web content pixels, for users who prefer white-on-black.
+// (Temporary, just during development and testing of this feature.)
+const char kInvertWebContent[]              = "invert-web-content";
+
 // Specifies the flags passed to JS engine
 const char kJavaScriptFlags[]               = "js-flags";