Add top-level Cobalt WebContentsObserver. (#4699)

b/384979128

cobalt/BUILD.gn

@@ -40,6 +40,8 @@ if (!is_android) {
       "cobalt_content_browser_client.h",
       "cobalt_main_delegate.cc",
       "cobalt_main_delegate.h",
+      "cobalt_web_contents_observer.cc",
+      "cobalt_web_contents_observer.h",
     ]
 
     defines = []

cobalt/android/BUILD.gn

@@ -268,6 +268,8 @@ shared_library("libcobalt_content_shell_content_view") {
     "//cobalt/cobalt_content_browser_client.h",
     "//cobalt/cobalt_main_delegate.cc",
     "//cobalt/cobalt_main_delegate.h",
+    "//cobalt/cobalt_web_contents_observer.cc",
+    "//cobalt/cobalt_web_contents_observer.h",
     "cobalt_library_loader.cc",
   ]
   configs -= [ "//build/config/android:hide_all_but_jni_onload" ]

cobalt/cobalt_content_browser_client.cc

@@ -91,4 +91,9 @@ void CobaltContentBrowserClient::OverrideWebkitPrefs(
   content::ShellContentBrowserClient::OverrideWebkitPrefs(web_contents, prefs);
 }
 
+void CobaltContentBrowserClient::OnWebContentsCreated(
+    content::WebContents* web_contents) {
+  web_contents_observer_.reset(new CobaltWebContentsObserver(web_contents));
+}
+
 }  // namespace cobalt

cobalt/cobalt_content_browser_client.h

@@ -15,6 +15,8 @@
 #ifndef COBALT_COBALT_CONTENT_BROWSER_CLIENT_H_
 #define COBALT_COBALT_CONTENT_BROWSER_CLIENT_H_
 
+#include "cobalt/cobalt_web_contents_observer.h"
+#include "content/public/browser/web_contents.h"
 #include "content/shell/browser/shell_content_browser_client.h"
 
 namespace cobalt {
@@ -31,6 +33,10 @@ class CobaltContentBrowserClient : public content::ShellContentBrowserClient {
   blink::UserAgentMetadata GetUserAgentMetadata() override;
   void OverrideWebkitPrefs(content::WebContents* web_contents,
                            blink::web_pref::WebPreferences* prefs) override;
+  void OnWebContentsCreated(content::WebContents* web_contents);
+
+ private:
+  std::unique_ptr<CobaltWebContentsObserver> web_contents_observer_;
 };
 
 }  // namespace cobalt

cobalt/cobalt_web_contents_observer.cc

@@ -0,0 +1,24 @@
+// Copyright 2025 The Cobalt Authors. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "cobalt/cobalt_web_contents_observer.h"
+
+namespace cobalt {
+
+// Placeholder for a WebContentsObserver override
+void CobaltWebContentsObserver::PrimaryMainDocumentElementAvailable() {
+  LOG(INFO) << "Cobalt::PrimaryMainDocumentElementAvailable";
+}
+
+}  // namespace cobalt

cobalt/cobalt_web_contents_observer.h

@@ -0,0 +1,33 @@
+// Copyright 2025 The Cobalt Authors. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef COBALT_COBALT_WEB_CONTENTS_OBSERVER_H_
+#define COBALT_COBALT_WEB_CONTENTS_OBSERVER_H_
+
+#include "content/public/browser/web_contents_observer.h"
+#include "content/shell/browser/shell_content_browser_client.h"
+
+namespace cobalt {
+
+class CobaltWebContentsObserver : public content::WebContentsObserver {
+ public:
+  explicit CobaltWebContentsObserver(content::WebContents* web_contents)
+      : content::WebContentsObserver(web_contents) {}
+
+  void PrimaryMainDocumentElementAvailable() override;
+};
+
+}  // namespace cobalt
+
+#endif  // COBALT_COBALT_WEB_CONTENTS_OBSERVER_H_