[DevTools] Rework DevToolsSession interaction with domain handlers.

content/browser/devtools/protocol/input_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/input_handler.h"
 
 #include <stddef.h>
 
 #include "base/strings/stringprintf.h"
 #include "base/strings/utf_string_conversions.h"
@@ skipping 162 matching lines @@
     callback->sendSuccess();
   } else {
     callback->sendFailure(Response::Error(
         base::StringPrintf("Synthetic scroll failed, result was %d", result)));
   }
 }
 
 }  // namespace
 
 InputHandler::InputHandler()
-    : host_(NULL),
+    : DevToolsDomainHandler(Input::Metainfo::domainName),
+      host_(nullptr),
       page_scale_factor_(1.0),
       last_id_(0),
       weak_factory_(this) {
 }
 
 InputHandler::~InputHandler() {
 }
 
 void InputHandler::SetRenderFrameHost(RenderFrameHostImpl* host) {
   host_ = host;
@@ skipping 339 matching lines @@
   for (int i = 0; i < count; i++) {
     host_->GetRenderWidgetHost()->QueueSyntheticGesture(
         SyntheticGesture::Create(gesture_params),
         base::Bind(&TapGestureResponse::OnGestureResult,
                    base::Unretained(response)));
   }
 }
 
 }  // namespace protocol
 }  // namespace content