Allow chromedriver to install an extension and get all installed extension IDs.

chrome/test/webdriver/webdriver_session.h

Index: chrome/test/webdriver/webdriver_session.h
diff --git a/chrome/test/webdriver/webdriver_session.h b/chrome/test/webdriver/webdriver_session.h
index c4edae8665e43c72f750a140e05116ba039e6ff9..e11f2fea2321126f06874bc1ffe0b9791f1c5e0c 100644
--- a/chrome/test/webdriver/webdriver_session.h
+++ b/chrome/test/webdriver/webdriver_session.h
@@ -307,7 +307,13 @@ class Session {
   Error* WaitForAllTabsToStopLoading();
 
   // Install packed extension at |path|.
-  Error* InstallExtension(const FilePath& path);
+  Error* InstallExtensionDeprecated(const FilePath& path);
+
+  // Get installed extensions IDs.
+  Error* GetInstalledExtensions(std::vector<std::string>* extension_ids);
+
+  // Install extension at |path|.
+  Error* InstallExtension(const FilePath& path, std::string* extension_id);
 
   const std::string& id() const;