[DevTools] Rework DevToolsSession interaction with domain handlers.

content/browser/devtools/protocol/inspector_handler.cc

 // Copyright 2014 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/inspector_handler.h"
 
+#include "content/browser/devtools/devtools_session.h"
 #include "content/browser/frame_host/render_frame_host_impl.h"
 
 namespace content {
 namespace protocol {
 
 InspectorHandler::InspectorHandler()
-    : host_(nullptr) {
+    : DevToolsDomainHandler(Inspector::Metainfo::domainName),
+      host_(nullptr) {
 }
 
 InspectorHandler::~InspectorHandler() {
 }
 
+// static
+InspectorHandler* InspectorHandler::FromSession(DevToolsSession* session) {
+  return static_cast<InspectorHandler*>(
+      session->GetHandlerByName(Inspector::Metainfo::domainName));
+}
+
 void InspectorHandler::Wire(UberDispatcher* dispatcher) {
   frontend_.reset(new Inspector::Frontend(dispatcher->channel()));
   Inspector::Dispatcher::wire(dispatcher, this);
 }
 
 void InspectorHandler::SetRenderFrameHost(RenderFrameHostImpl* host) {
   host_ = host;
 }
 
 void InspectorHandler::TargetCrashed() {
   frontend_->TargetCrashed();
 }
 
 void InspectorHandler::TargetDetached(const std::string& reason) {
   frontend_->Detached(reason);
 }
 
 Response InspectorHandler::Enable() {
   if (host_ && !host_->IsRenderFrameLive())
     frontend_->TargetCrashed();
   return Response::OK();
 }
 
 Response InspectorHandler::Disable() {
   return Response::OK();
 }
 
 }  // namespace protocol
 }  // namespace content