Add a function for determining if official Google Chrome API key is used.

google_apis/google_api_keys.h

Index: google_apis/google_api_keys.h
diff --git a/google_apis/google_api_keys.h b/google_apis/google_api_keys.h
index 8f4bc7e9cacded2d94d0f9c697b87cfb0de42d08..5acdf263a6ffb9c58c191df6accbc567c6040abf 100644
--- a/google_apis/google_api_keys.h
+++ b/google_apis/google_api_keys.h
@@ -90,6 +90,10 @@ std::string GetOAuth2ClientID(OAuth2Client client);
 // in, e.g. URL-escaped if you use it in a URL.
 std::string GetOAuth2ClientSecret(OAuth2Client client);
 
+// Returns if the API key using in the current build is the one for official
+// Google Chrome.
+bool IsGoogleChromeAPIKeyUsed();
+
 }  // namespace google_apis
 
 #endif  // GOOGLE_APIS_GOOGLE_API_KEYS_H_