Reduce usage of FOR_EACH_OBSERVER macro in content/browser

content/browser/frame_host/frame_tree_node.cc

Index: content/browser/frame_host/frame_tree_node.cc
diff --git a/content/browser/frame_host/frame_tree_node.cc b/content/browser/frame_host/frame_tree_node.cc
index 9d6eac59956f040c18ba9478aa7efcc9d024b4c9..3f789ef905cca6578e1778ef5eea8944e8e3c3e8 100644
--- a/content/browser/frame_host/frame_tree_node.cc
+++ b/content/browser/frame_host/frame_tree_node.cc
@@ -121,7 +121,8 @@ FrameTreeNode::FrameTreeNode(FrameTree* frame_tree,
 FrameTreeNode::~FrameTreeNode() {
   std::vector<std::unique_ptr<FrameTreeNode>>().swap(children_);
   frame_tree_->FrameRemoved(this);
-  FOR_EACH_OBSERVER(Observer, observers_, OnFrameTreeNodeDestroyed(this));
+  for (auto& observer : observers_)
+    observer.OnFrameTreeNodeDestroyed(this);
 
   if (opener_)
     opener_->RemoveObserver(opener_observer_.get());
@@ -465,7 +466,8 @@ bool FrameTreeNode::StopLoading() {
 
 void FrameTreeNode::DidFocus() {
   last_focus_time_ = base::TimeTicks::Now();
-  FOR_EACH_OBSERVER(Observer, observers_, OnFrameTreeNodeFocused(this));
+  for (auto& observer : observers_)
+    observer.OnFrameTreeNodeFocused(this);
 }
 
 void FrameTreeNode::BeforeUnloadCanceled() {