Disable extension Panels on Dev and Canary, except for the whitelist

extensions/common/constants.h

Index: extensions/common/constants.h
diff --git a/extensions/common/constants.h b/extensions/common/constants.h
index b4a546bd7f53d1040cae669bfdbe83882ce56402..702095b9ecb2f73fd0b513acdb12c529afb5fd86 100644
--- a/extensions/common/constants.h
+++ b/extensions/common/constants.h
@@ -223,6 +223,12 @@ extern const char kQuickOfficeExtensionId[];
 // The extension id used for testing mimeHandlerPrivate.
 extern const char kMimeHandlerPrivateTestExtensionId[];
 
+// The extension id for the production version of Hangouts.
+extern const char kProdHangoutsExtensionId[];
+
+// Extension ids used by Hangouts.
+extern const char* const kHangoutsExtensionIds[6];
+
 }  // namespace extension_misc
 
 #endif  // EXTENSIONS_COMMON_CONSTANTS_H_