Remove RenderFrameProxyHost creation from DiscardUnusedFrame().

Removing proxy creation code that wasn't getting called,
because we always create proxies for speculative RFHs since
r501081. Also removed related logic that appears to have only
been there for proxies that were created in this function.

Bug: 1015882
Change-Id: I22c9a735254c3e2cf0068c9914ab66815a40dd11
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2481905
Commit-Queue: Aaron Colwell <acolwell@chromium.org>
Reviewed-by: Charlie Reis <creis@chromium.org>
Reviewed-by: Alex Moshchuk <alexmos@chromium.org>
Cr-Commit-Position: refs/heads/master@{#819048}

content/browser/renderer_host/render_frame_host_manager.cc

@@ -599,33 +599,21 @@ void RenderFrameHostManager::DiscardUnusedFrame(
   // that it is replaced by a RenderFrameProxyHost to allow other frames to
   // communicate to this frame.
   SiteInstanceImpl* site_instance = render_frame_host->GetSiteInstance();
-  RenderViewHostImpl* rvh = render_frame_host->render_view_host();
   RenderFrameProxyHost* proxy = nullptr;
   if (site_instance->HasSite() && site_instance->active_frame_count() > 1) {
-    // If a proxy already exists for the |site_instance|, just reuse it instead
-    // of creating a new one. There is no need to call Unload() on the
-    // |render_frame_host|, as this method is only called to discard a pending
-    // or speculative RenderFrameHost, i.e. one that has never hosted an actual
-    // document.
+    // A proxy already exists for the |site_instance| so just reuse it. There is
+    // no need to call Unload() on the |render_frame_host|, as this method is
+    // only called to discard a pending or speculative RenderFrameHost, i.e. one
+    // that has never hosted an actual document.
     proxy = GetRenderFrameProxyHost(site_instance);
-    if (!proxy)
-      proxy = CreateRenderFrameProxyHost(site_instance, rvh);
+    CHECK(proxy);
   }
 
-  // Doing this is important in the case where the replacement proxy is created
-  // above, as the RenderViewHost will continue to exist and should be
-  // considered inactive.  When there's no replacement proxy, this doesn't
-  // really matter, as the RenderViewHost will be destroyed shortly, since
-  // |render_frame_host| is its last active frame and will be deleted below.
-  // See https://crbug.com/627400.
-  if (frame_tree_node_->IsMainFrame())
-    rvh->SetMainFrameRoutingId(MSG_ROUTING_NONE);
-
   render_frame_host.reset();
 
-  // If a new RenderFrameProxyHost was created above, or if the old proxy isn't
-  // live, create the RenderFrameProxy in the renderer, so that other frames
-  // can still communicate with this frame.  See https://crbug.com/653746.
+  // If the old proxy isn't live, create the RenderFrameProxy in the renderer,
+  // so that other frames can still communicate with this frame.  See
+  // https://crbug.com/653746.
   if (proxy && !proxy->is_render_frame_proxy_live())
     proxy->InitRenderFrameProxy();
 }