Expose the full API for attaching devtools clients:

headless/lib/browser/headless_web_contents_impl.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "headless/lib/browser/headless_web_contents_impl.h"
 
 #include <string>
 #include <utility>
 
 #include "base/bind.h"
@@ skipping 222 matching lines @@
 void HeadlessWebContentsImpl::RenderProcessHostDestroyed(
     content::RenderProcessHost* host) {
   DCHECK_EQ(render_process_host_, host);
   render_process_host_ = nullptr;
 }
 
 HeadlessDevToolsTarget* HeadlessWebContentsImpl::GetDevToolsTarget() {
   return web_contents()->GetMainFrame()->IsRenderFrameLive() ? this : nullptr;
 }
 
-void HeadlessWebContentsImpl::AttachClient(HeadlessDevToolsClient* client) {
-  HeadlessDevToolsClientImpl::From(client)->AttachToHost(agent_host_.get());
+bool HeadlessWebContentsImpl::AttachClient(HeadlessDevToolsClient* client) {
+  return HeadlessDevToolsClientImpl::From(client)->AttachToHost(
+      agent_host_.get());
+}
+
+void HeadlessWebContentsImpl::ForceAttachClient(
+    HeadlessDevToolsClient* client) {
+  HeadlessDevToolsClientImpl::From(client)->ForceAttachToHost(
+      agent_host_.get());
 }
 
 void HeadlessWebContentsImpl::DetachClient(HeadlessDevToolsClient* client) {
   DCHECK(agent_host_);
   HeadlessDevToolsClientImpl::From(client)->DetachFromHost(agent_host_.get());
 }
 
+bool HeadlessWebContentsImpl::IsAttached() {
+  DCHECK(agent_host_);
+  return agent_host_->IsAttached();
+}
+
 content::WebContents* HeadlessWebContentsImpl::web_contents() const {
   return web_contents_.get();
 }
 
 HeadlessBrowserImpl* HeadlessWebContentsImpl::browser() const {
   return browser_context_->browser();
 }
 
 HeadlessBrowserContextImpl* HeadlessWebContentsImpl::browser_context() const {
   return browser_context_;
@@ skipping 35 matching lines @@
 HeadlessWebContents::Builder::MojoService::MojoService() {}
 
 HeadlessWebContents::Builder::MojoService::MojoService(
     const std::string& service_name,
     const base::Callback<void(mojo::ScopedMessagePipeHandle)>& service_factory)
     : service_name(service_name), service_factory(service_factory) {}
 
 HeadlessWebContents::Builder::MojoService::~MojoService() {}
 
 }  // namespace headless