Add commands to manage tabs and contexts to Browser Domain

headless/lib/browser/headless_browser_impl.cc

Index: headless/lib/browser/headless_browser_impl.cc
diff --git a/headless/lib/browser/headless_browser_impl.cc b/headless/lib/browser/headless_browser_impl.cc
index a3eb1ba37406e9ec9a87b979cff65bb23781b0ed..f7f54d3de0c75e7a593b91c968c0b433682959cb 100644
--- a/headless/lib/browser/headless_browser_impl.cc
+++ b/headless/lib/browser/headless_browser_impl.cc
@@ -65,6 +65,14 @@ HeadlessBrowserImpl::CreateBrowserContextBuilder() {
   return HeadlessBrowserContext::Builder(this);
 }
 
+void HeadlessBrowserImpl::AddObserver(Observer* observer) {
+  observers_.insert(observer);
+}
+
+void HeadlessBrowserImpl::RemoveObserver(Observer* observer) {
+  observers_.erase(observer);
+}
+
 HeadlessWebContents* HeadlessBrowserImpl::CreateWebContents(
     HeadlessWebContents::Builder* builder) {
   DCHECK(BrowserMainThread()->BelongsToCurrentThread());
@@ -108,7 +116,7 @@ std::vector<HeadlessWebContents*> HeadlessBrowserImpl::GetAllWebContents() {
   result.reserve(web_contents_.size());
 
   for (const auto& web_contents_pair : web_contents_) {
-    result.push_back(web_contents_pair.first);
+    result.push_back(web_contents_pair.second.get());
   }
 
   return result;
@@ -142,17 +150,30 @@ void HeadlessBrowserImpl::RunOnStartCallback() {
 
 HeadlessWebContentsImpl* HeadlessBrowserImpl::RegisterWebContents(
     std::unique_ptr<HeadlessWebContentsImpl> web_contents) {
+  DCHECK(BrowserMainThread()->BelongsToCurrentThread());
   DCHECK(web_contents);
   HeadlessWebContentsImpl* unowned_web_contents = web_contents.get();
   web_contents_[unowned_web_contents] = std::move(web_contents);
+  for (auto it = observers_.begin(); it != observers_.end();) {
+    // Pre-increment it because the observer may unregister itself.
+    Observer* observer = *it++;
+    observer->HeadlessWebContentsCreated(unowned_web_contents);
+  }
   return unowned_web_contents;
 }
 
 void HeadlessBrowserImpl::DestroyWebContents(
     HeadlessWebContentsImpl* web_contents) {
-  auto it = web_contents_.find(web_contents);
-  DCHECK(it != web_contents_.end());
-  web_contents_.erase(it);
+  DCHECK(BrowserMainThread()->BelongsToCurrentThread());
+  auto find_it = web_contents_.find(web_contents);
+  DCHECK(find_it != web_contents_.end());
+  HeadlessWebContents* headless_web_contents = find_it->second.get();
+  web_contents_.erase(find_it);
+  for (auto it = observers_.begin(); it != observers_.end();) {
+    // Pre-increment it because the observer may unregister itself.
+    Observer* observer = *it++;
+    observer->HeadlessWebContentsDestroyed(headless_web_contents);
+  }
 }
 
 void HeadlessBrowserImpl::SetOptionsForTesting(