This is essentially just a similarity=50 version of https://codereview.chromium.org/95133002/ and i…

extensions/common/switches.cc

Index: extensions/common/switches.cc
diff --git a/extensions/common/switches.cc b/extensions/common/switches.cc
index 6e8e2713d8ac7d9c5428f0b8e81e008b74d12fe6..2c6a39be27d744573dc4e1fed1197a907eeca230 100644
--- a/extensions/common/switches.cc
+++ b/extensions/common/switches.cc
@@ -50,6 +50,9 @@ const char kEventPageSuspendingTime[]       = "event-page-unloading-time";
 // manifest.
 const char kExtensionsOnChromeURLs[] = "extensions-on-chrome-urls";
 
+// Whether to force developer mode extensions highlighting.
+const char kForceDevModeHighlighting[] = "force-dev-mode-highlighting";
+
 // Enables setting global commands through the Extensions Commands API.
 const char kGlobalCommands[] = "global-commands";