Move kEnableExperimentalExtensionApis switch to extensions/common/switches.cc.

extensions/common/switches.cc

Index: extensions/common/switches.cc
diff --git a/extensions/common/switches.cc b/extensions/common/switches.cc
index f85ff4b9f85514c82f13b1031b4e86db26517090..228a557fa588bd984dac89028cfd3150cfe493b7 100644
--- a/extensions/common/switches.cc
+++ b/extensions/common/switches.cc
@@ -18,6 +18,10 @@ const char kAllowLegacyExtensionManifests[] =
 // automation testing of the gallery.
 const char kAllowScriptingGallery[]         = "allow-scripting-gallery";
 
+// Enables extension APIs that are in development.
+const char kEnableExperimentalExtensionApis[] =
+    "enable-experimental-extension-apis";
+
 // Enables extensions running scripts on chrome:// URLs.
 // Extensions still need to explicitly request access to chrome:// URLs in the
 // manifest.