[Chromedriver] Chromedriver should handle unexpected alert automatically.

chrome/test/chromedriver/chrome/chrome.h

Index: chrome/test/chromedriver/chrome/chrome.h
diff --git a/chrome/test/chromedriver/chrome/chrome.h b/chrome/test/chromedriver/chrome/chrome.h
index 14251c7c160e08a133dd881027beb79c8fb4d417..73251448d1ed13ee63377fba9227a69091d8d94b 100644
--- a/chrome/test/chromedriver/chrome/chrome.h
+++ b/chrome/test/chromedriver/chrome/chrome.h
@@ -53,6 +53,9 @@ class Chrome {
   // Return the page load strategy for this session.
   virtual std::string page_load_strategy() const = 0;
 
+  // Return the unexpected alert behaviour.
+  virtual std::string UnexpectedAlertBehaviour() const = 0;
+
   // Quits Chrome.
   virtual Status Quit() = 0;
 };