[Blimp] Creates engine tab class to handle tab related operations.

blimp/engine/session/page_load_tracker.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 "blimp/engine/session/page_load_tracker.h"
 
 #include "content/public/browser/render_widget_host_view.h"
 
 namespace blimp {
 namespace engine {
 
 namespace {
 
 content::RenderWidgetHost* GetRenderWidgetHostIfMainFrame(
     content::RenderFrameHost* render_frame_host) {
   if (render_frame_host->GetParent() != nullptr)
     return nullptr;
 
   return render_frame_host->GetView()->GetRenderWidgetHost();
 }
 
 }  // namespace
 
 PageLoadTracker::PageLoadTracker(content::WebContents* web_contents,
                                  PageLoadTrackerClient* client)
     : client_(client) {
+  DCHECK(web_contents);
   Observe(web_contents);
 }
 
 PageLoadTracker::~PageLoadTracker() {}
 
 void PageLoadTracker::DidStartProvisionalLoadForFrame(
     content::RenderFrameHost* render_frame_host,
     const GURL& validated_url,
     bool is_error_page,
     bool is_iframe_srcdoc) {
@@ skipping 57 matching lines @@
     render_widget_load_status_.erase(it);
   }
 }
 
 bool PageLoadTracker::LoadStatus::Loaded() const {
   return page_loaded && did_first_paint;
 }
 
 }  // namespace engine
 }  // namespace blimp