base: Remove the string logging from CHECK().

content/browser/frame_host/render_frame_host_manager.cc

Index: content/browser/frame_host/render_frame_host_manager.cc
diff --git a/content/browser/frame_host/render_frame_host_manager.cc b/content/browser/frame_host/render_frame_host_manager.cc
index 59cbe436c80a945cff6f16a1e98cea75ad0b679d..a95162e4deb05ba4e681f2481aa1a9edba8dbf29 100644
--- a/content/browser/frame_host/render_frame_host_manager.cc
+++ b/content/browser/frame_host/render_frame_host_manager.cc
@@ -1059,8 +1059,8 @@ RenderFrameProxyHost* RenderFrameHostManager::CreateRenderFrameProxyHost(
     SiteInstance* site_instance,
     RenderViewHostImpl* rvh) {
   int site_instance_id = site_instance->GetId();
-  CHECK(proxy_hosts_.find(site_instance_id) == proxy_hosts_.end())
-      << "A proxy already existed for this SiteInstance.";
+  // A proxy already existed for this SiteInstance.
+  CHECK(proxy_hosts_.find(site_instance_id) == proxy_hosts_.end());
   RenderFrameProxyHost* proxy_host =
       new RenderFrameProxyHost(site_instance, rvh, frame_tree_node_);
   proxy_hosts_[site_instance_id] = base::WrapUnique(proxy_host);