Introduce RenderFrame::IsMainFrame and clean up a few things.

chrome/renderer/chrome_content_renderer_client.cc

Index: chrome/renderer/chrome_content_renderer_client.cc
diff --git a/chrome/renderer/chrome_content_renderer_client.cc b/chrome/renderer/chrome_content_renderer_client.cc
index 8c2a38d9b016b931934bcecd0de844d47474936c..170b23f78f815c99d59ab64fd6f028b4dcb3e702 100644
--- a/chrome/renderer/chrome_content_renderer_client.cc
+++ b/chrome/renderer/chrome_content_renderer_client.cc
@@ -550,27 +550,21 @@ void ChromeContentRendererClient::RenderFrameCreated(
   new nacl::NaClHelper(render_frame);
 #endif
 
-  // TODO(jam): when the frame tree moves into content and parent() works at
-  // RenderFrame construction, simplify this by just checking parent().
-  if (render_frame->GetRenderView()->GetMainRenderFrame() != render_frame) {
-    // Avoid any race conditions from having the browser tell subframes that
-    // they're prerendering.
-    if (prerender::PrerenderHelper::IsPrerendering(
-            render_frame->GetRenderView()->GetMainRenderFrame())) {
-      new prerender::PrerenderHelper(render_frame);
-    }
-  }
-
-  if (render_frame->GetRenderView()->GetMainRenderFrame() == render_frame) {
+  if (render_frame->IsMainFrame()) {
     // Only attach NetErrorHelper to the main frame, since only the main frame
     // should get error pages.
     new NetErrorHelper(render_frame);
-  }
 
-  if (render_frame->GetWebFrame()->parent() == nullptr) {
     // Only attach MainRenderFrameObserver to the main frame, since
     // we only want to log page load metrics for the main frame.
     new page_load_metrics::MetricsRenderFrameObserver(render_frame);
+  } else {
+    // Avoid any race conditions from having the browser tell subframes that
+    // they're prerendering.
+    if (prerender::PrerenderHelper::IsPrerendering(
+            render_frame->GetRenderView()->GetMainRenderFrame())) {
+      new prerender::PrerenderHelper(render_frame);
+    }
   }
 
   // Set up a mojo service to test if this page is a distiller page.