Allow chrome.debugger API to attach to extension background pages.

chrome/browser/extensions/api/debugger/debugger_api_constants.h

Index: chrome/browser/extensions/api/debugger/debugger_api_constants.h
diff --git a/chrome/browser/extensions/api/debugger/debugger_api_constants.h b/chrome/browser/extensions/api/debugger/debugger_api_constants.h
index 67e605e9ef494c1393d9f1b9f881fef2a3206565..f3c400e0cc0aa6950ae21d36c5b0d5f60605276e 100644
--- a/chrome/browser/extensions/api/debugger/debugger_api_constants.h
+++ b/chrome/browser/extensions/api/debugger/debugger_api_constants.h
@@ -16,9 +16,15 @@ extern const char kOnDetach[];
 // Errors.
 extern const char kAlreadyAttachedError[];
 extern const char kAttachToWebUIError[];
-extern const char kNoTabError[];
+extern const char kNoTargetError[];
+extern const char kInvalidTargetError[];
 extern const char kNotAttachedError[];
 extern const char kProtocolVersionNotSupportedError[];
+extern const char kSilentDebuggingRequired[];
+
+// Target types.
+extern const char kTabTargetType[];
+extern const char kExtensionTargetType[];
 
 }  // namespace debugger_api_constants