Add commands to manage tabs and contexts to Browser Domain

headless/public/headless_browser.h

Index: headless/public/headless_browser.h
diff --git a/headless/public/headless_browser.h b/headless/public/headless_browser.h
index 2e9145153aecb42a4f126481436003fb8e0a6cbe..aad40615272eefb1a4824aa7b9c88c11c628bf75 100644
--- a/headless/public/headless_browser.h
+++ b/headless/public/headless_browser.h
@@ -38,6 +38,30 @@ class HEADLESS_EXPORT HeadlessBrowser {
  public:
   struct Options;
 
+  class HEADLESS_EXPORT Observer {

[Sami, 2016/07/04 15:28:54]

Could we instead add a getter that turns a target id into a HeadlessWebContents
object? If we want these to be events, we could probably add them to the
devtools browser domain.

[alex clarke (OOO till 29th), 2016/07/04 16:33:59]

I only really added it for testing when I had a different way of closing the
page which made it async. I think we can live without it now.

+   public:
+    // All the following notifications will be called on browser main thread.
+
+    virtual void HeadlessWebContentsCreated(HeadlessWebContents* web_contents) {
+    }
+
+    // Note |web_contents| has been deleted, do not dereference.
+    virtual void HeadlessWebContentsDestroyed(
+        HeadlessWebContents* web_contents) {}
+
+   protected:
+    Observer() {}
+    virtual ~Observer() {}
+
+   private:
+    DISALLOW_COPY_AND_ASSIGN(Observer);
+  };
+
+  // Add or remove an observer to receive events from this HeadlessBrowser.
+  // |observer| must outlive this class or be removed prior to being destroyed.
+  virtual void AddObserver(Observer* observer) = 0;
+  virtual void RemoveObserver(Observer* observer) = 0;
+
   // Open a new tab. Returns a builder object which can be used to set
   // properties for the new tab.
   virtual HeadlessWebContents::Builder CreateWebContentsBuilder() = 0;