Add commands to manage tabs and contexts to Browser Domain

headless/lib/browser/headless_browser_impl.h

Index: headless/lib/browser/headless_browser_impl.h
diff --git a/headless/lib/browser/headless_browser_impl.h b/headless/lib/browser/headless_browser_impl.h
index 68dc676e5dd9acd9d07ebe90bb74f6fe92d4131a..9173807e81192fea2c1ce33e20346fa9294e0ee1 100644
--- a/headless/lib/browser/headless_browser_impl.h
+++ b/headless/lib/browser/headless_browser_impl.h
@@ -8,6 +8,7 @@
 #include "headless/public/headless_browser.h"
 
 #include <memory>
+#include <set>
 #include <unordered_map>
 #include <vector>
 
@@ -34,6 +35,8 @@ class HeadlessBrowserImpl : public HeadlessBrowser {
   ~HeadlessBrowserImpl() override;
 
   // HeadlessBrowser implementation:
+  void AddObserver(Observer* observer) override;
+  void RemoveObserver(Observer* observer) override;
   HeadlessWebContents::Builder CreateWebContentsBuilder() override;
   HeadlessBrowserContext::Builder CreateBrowserContextBuilder() override;
   HeadlessWebContents* CreateWebContents(const GURL& initial_url,
@@ -76,6 +79,8 @@ class HeadlessBrowserImpl : public HeadlessBrowser {
   std::unordered_map<HeadlessWebContents*, std::unique_ptr<HeadlessWebContents>>
       web_contents_;
 
+  std::set<HeadlessBrowser::Observer*> observers_;
+
  private:
   DISALLOW_COPY_AND_ASSIGN(HeadlessBrowserImpl);
 };