Upstream iOS web code.

ios/web/web_state/web_state_observer.cc

Index: ios/web/web_state/web_state_observer.cc
diff --git a/ios/web/web_state/web_state_observer.cc b/ios/web/web_state/web_state_observer.cc
new file mode 100644
index 0000000000000000000000000000000000000000..c5c1ab79fa2dc475c7004a9fabead8f937c0139b
--- /dev/null
+++ b/ios/web/web_state/web_state_observer.cc
@@ -0,0 +1,42 @@
+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "ios/web/public/web_state/web_state_observer.h"
+
+#include "ios/public/provider/web/web_state.h"
+#include "ios/web/public/load_committed_details.h"
+
+namespace web {
+
+WebStateObserver::WebStateObserver(ios::WebState* web_state)
+    : web_state_(nullptr) {
+  Observe(web_state);
+}
+
+WebStateObserver::WebStateObserver() : web_state_(nullptr) {
+}
+
+WebStateObserver::~WebStateObserver() {
+  if (web_state_)
+    web_state_->RemoveObserver(this);
+}
+
+void WebStateObserver::Observe(ios::WebState* web_state) {
+  if (web_state == web_state_) {
+    // Early exit to avoid infinite loops if we're in the middle of a callback.
+    return;
+  }
+  if (web_state_)
+    web_state_->RemoveObserver(this);
+  web_state_ = web_state;
+  if (web_state_)
+    web_state_->AddObserver(this);
+}
+
+void WebStateObserver::ResetWebState() {
+  web_state_->RemoveObserver(this);
+  web_state_ = NULL;

[stuartmorgan, 2014/12/04 23:22:58]

Could you change this to nullptr?

+}
+
+}  // namespace web