[DevTools] Rework DevToolsSession interaction with domain handlers.

content/browser/devtools/protocol/target_handler.cc

 // Copyright 2016 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 "content/browser/devtools/protocol/target_handler.h"
 
 #include "content/browser/devtools/devtools_manager.h"
+#include "content/browser/devtools/devtools_session.h"
 #include "content/browser/devtools/service_worker_devtools_agent_host.h"
 #include "content/browser/frame_host/frame_tree.h"
 #include "content/browser/frame_host/frame_tree_node.h"
 #include "content/browser/frame_host/render_frame_host_impl.h"
 
 namespace content {
 namespace protocol {
 
 namespace {
 
@@ skipping 68 matching lines @@
       .SetTargetId(host->GetId())
       .SetTitle(host->GetTitle())
       .SetUrl(host->GetURL().spec())
       .SetType(host->GetType())
       .Build();
 }
 
 }  // namespace
 
 TargetHandler::TargetHandler()
-    : discover_(false),
+    : DevToolsDomainHandler(Target::Metainfo::domainName),
+      discover_(false),
       auto_attach_(false),
       wait_for_debugger_on_start_(false),
       attach_to_frames_(false),
       render_frame_host_(nullptr) {
 }
 
 TargetHandler::~TargetHandler() {
 }
 
+// static
+TargetHandler* TargetHandler::FromSession(DevToolsSession* session) {
+  return static_cast<TargetHandler*>(
+      session->GetHandlerByName(Target::Metainfo::domainName));
+}
+
 void TargetHandler::Wire(UberDispatcher* dispatcher) {
   frontend_.reset(new Target::Frontend(dispatcher->channel()));
   Target::Dispatcher::wire(dispatcher, this);
 }
 
 void TargetHandler::SetRenderFrameHost(RenderFrameHostImpl* render_frame_host) {
   render_frame_host_ = render_frame_host;
   UpdateFrames();
 }
 
@@ skipping 332 matching lines @@
   UpdateServiceWorkers();
 }
 
 void TargetHandler::WorkerDestroyed(
     ServiceWorkerDevToolsAgentHost* host) {
   UpdateServiceWorkers();
 }
 
 }  // namespace protocol
 }  // namespace content