Add ContentBrowserClient::OpenURL to allow tab opening wo/ WebContents.

content/public/browser/content_browser_client.cc

Index: content/public/browser/content_browser_client.cc
diff --git a/content/public/browser/content_browser_client.cc b/content/public/browser/content_browser_client.cc
index 32d29d735124d905d2edc9792c9d25e1cf397722..59c1937794fcc6063ca07a707d8abe8756445e73 100644
--- a/content/public/browser/content_browser_client.cc
+++ b/content/public/browser/content_browser_client.cc
@@ -336,6 +336,11 @@ bool ContentBrowserClient::CheckMediaAccessPermission(
   return false;
 }
 
+WebContents* ContentBrowserClient::OpenURL(BrowserContext* browser_context,
+                                           const OpenURLParams& params) {
+  return nullptr;
+}
+
 #if defined(OS_WIN)
 const wchar_t* ContentBrowserClient::GetResourceDllName() {
   return nullptr;