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

content/public/browser/content_browser_client.h

Index: content/public/browser/content_browser_client.h
diff --git a/content/public/browser/content_browser_client.h b/content/public/browser/content_browser_client.h
index e5f40c49df315be90985403a2285daf5c5517490..1b32162f2779d207a1ba13eadc77942ede9309c9 100644
--- a/content/public/browser/content_browser_client.h
+++ b/content/public/browser/content_browser_client.h
@@ -104,6 +104,7 @@ class SpeechRecognitionManagerDelegate;
 class WebContents;
 class WebContentsViewDelegate;
 struct MainFunctionParams;
+struct OpenURLParams;
 struct Referrer;
 struct WebPreferences;
 
@@ -588,6 +589,11 @@ class CONTENT_EXPORT ContentBrowserClient {
   // RenderProcessHost.
   virtual void OverrideRenderProcessMojoServices(ServiceRegistry* registry) {}
 
+  // Allows programmatic opening of a new tab/window without going through
+  // another WebContents. For example, from a Worker.
+  virtual WebContents* OpenURL(BrowserContext* browser_context,
+                               const OpenURLParams& params);
+
 #if defined(OS_POSIX) && !defined(OS_MACOSX)
   // Populates |mappings| with all files that need to be mapped before launching
   // a child process.