Allow api::WebContents to fully wrap an existing content::WebContents.

- Add an overload to `WebContents::CreateFrom` that accepts a type parameter. If
  type is `REMOTE`, initialization is the same as before(a thin wrapper). If
  not, the `api::WebContents` will be fully initialized, as if it was created by
  `api::WebContents::Create`.
- Move common initialization code to `InitWithSessionAndOptions`.

atom/browser/api/atom_api_web_contents.cc

@@ -258,17 +258,25 @@ void OnCapturePageDone(base::Callback<void(const gfx::Image&)> callback,
 }  // namespace
 
 WebContents::WebContents(v8::Isolate* isolate,
-                         content::WebContents* web_contents)
+                         content::WebContents* web_contents,
+                         Type type)
     : content::WebContentsObserver(web_contents),
       embedder_(nullptr),
-      type_(REMOTE),
+      type_(type),
       request_id_(0),
       background_throttling_(true),
       enable_devtools_(true) {
-  web_contents->SetUserAgentOverride(GetBrowserContext()->GetUserAgent());
 
+  if (type == REMOTE) {
+    web_contents->SetUserAgentOverride(GetBrowserContext()->GetUserAgent());
     Init(isolate);
     AttachAsUserData(web_contents);
+  } else {
+    const mate::Dictionary options = mate::Dictionary::CreateEmpty(isolate);
+    auto session = Session::CreateFrom(isolate, GetBrowserContext());
+    session_.Reset(isolate, session.ToV8());
+    InitWithSessionAndOptions(isolate, web_contents, session, options);
+  }
 }
 
 WebContents::WebContents(v8::Isolate* isolate,
@@ -336,6 +344,13 @@ WebContents::WebContents(v8::Isolate* isolate,
     web_contents = content::WebContents::Create(params);
   }
 
+  InitWithSessionAndOptions(isolate, web_contents, session, options);
+}
+
+void WebContents::InitWithSessionAndOptions(v8::Isolate* isolate,
+                                            content::WebContents *web_contents,
+                                            mate::Handle<api::Session> session,
+                                            const mate::Dictionary& options) {
   Observe(web_contents);
   InitWithWebContents(web_contents, session->browser_context());
 
@@ -1605,7 +1620,15 @@ mate::Handle<WebContents> WebContents::CreateFrom(
     return mate::CreateHandle(isolate, static_cast<WebContents*>(existing));
 
   // Otherwise create a new WebContents wrapper object.
-  return mate::CreateHandle(isolate, new WebContents(isolate, web_contents));
+  return mate::CreateHandle(isolate, new WebContents(isolate, web_contents,
+        REMOTE));
+}
+
+mate::Handle<WebContents> WebContents::CreateFrom(
+    v8::Isolate* isolate, content::WebContents* web_contents, Type type) {
+  // Otherwise create a new WebContents wrapper object.
+  return mate::CreateHandle(isolate, new WebContents(isolate, web_contents,
+        type));
 }
 
 // static

atom/browser/api/atom_api_web_contents.h

@@ -58,6 +58,8 @@ class WebContents : public mate::TrackableObject<WebContents>,
   // Create from an existing WebContents.
   static mate::Handle<WebContents> CreateFrom(
       v8::Isolate* isolate, content::WebContents* web_contents);
+  static mate::Handle<WebContents> CreateFrom(
+      v8::Isolate* isolate, content::WebContents* web_contents, Type type);
 
   // Create a new WebContents.
   static mate::Handle<WebContents> Create(
@@ -191,10 +193,17 @@ class WebContents : public mate::TrackableObject<WebContents>,
   v8::Local<v8::Value> Debugger(v8::Isolate* isolate);
 
  protected:
-  WebContents(v8::Isolate* isolate, content::WebContents* web_contents);
+  WebContents(v8::Isolate* isolate,
+              content::WebContents* web_contents,
+              Type type);
   WebContents(v8::Isolate* isolate, const mate::Dictionary& options);
   ~WebContents();
 
+  void InitWithSessionAndOptions(v8::Isolate* isolate,
+                                 content::WebContents *web_contents,
+                                 mate::Handle<class Session> session,
+                                 const mate::Dictionary& options);
+
   // content::WebContentsDelegate:
   bool AddMessageToConsole(content::WebContents* source,
                            int32_t level,