Do not reinvent the wheel / use content APIs to find a frame by name.

content/browser/webui/web_ui_impl.cc

Index: content/browser/webui/web_ui_impl.cc
diff --git a/content/browser/webui/web_ui_impl.cc b/content/browser/webui/web_ui_impl.cc
index c024bc82b8b20a0ef06f6a5aa0061f25bdf23437..c5e8a7a215e77094699ee597d1986d846e705437 100644
--- a/content/browser/webui/web_ui_impl.cc
+++ b/content/browser/webui/web_ui_impl.cc
@@ -11,6 +11,9 @@
 #include "base/strings/utf_string_conversions.h"
 #include "base/values.h"
 #include "content/browser/child_process_security_policy_impl.h"
+#include "content/browser/frame_host/frame_tree.h"
+#include "content/browser/frame_host/frame_tree_node.h"
+#include "content/browser/frame_host/render_frame_host_impl.h"
 #include "content/browser/renderer_host/dip_util.h"
 #include "content/browser/renderer_host/render_process_host_impl.h"
 #include "content/browser/web_contents/web_contents_impl.h"
@@ -280,24 +283,10 @@ RenderFrameHost* WebUIImpl::TargetFrame() {
   if (frame_name_.empty())
     return web_contents_->GetMainFrame();
 
-  std::set<RenderFrameHost*> frame_set;
-  web_contents_->ForEachFrame(base::Bind(&WebUIImpl::AddToSetIfFrameNameMatches,
-                                         base::Unretained(this),
-                                         &frame_set));
-
-  // It happens that some sub-pages attempt to send JavaScript messages before
-  // their frames are loaded.
-  DCHECK_GE(1U, frame_set.size());
-  if (frame_set.empty())
-    return NULL;
-  return *frame_set.begin();
-}
-
-void WebUIImpl::AddToSetIfFrameNameMatches(
-    std::set<RenderFrameHost*>* frame_set,
-    RenderFrameHost* host) {
-  if (host->GetFrameName() == frame_name_)
-    frame_set->insert(host);
+  return static_cast<WebContentsImpl*>(web_contents_)
+      ->GetFrameTree()
+      ->FindByName(frame_name_)
+      ->current_frame_host();

[ncarter (slow), 2017/04/27 22:03:42]

We need to handle a null return value of FindByName, and return nullptr. Looks
like some of the callers of TargetFrame handle a null return value.

[Łukasz Anforowicz, 2017/04/27 22:59:28]

Ooops.  Done.

(I first wrote returning of FindByName and mentally noted that it returning null
matches what the old code does;  I didn't recheck this when adding
->current_frame_host() later on... :-/ ;  at least the browser tests caught this
:-).

 }
 
 void WebUIImpl::DisallowJavascriptOnAllHandlers() {