Return unique_ptr from WebClient::CreateWebMainParts()

ios/web/shell/shell_web_client.h

Index: ios/web/shell/shell_web_client.h
diff --git a/ios/web/shell/shell_web_client.h b/ios/web/shell/shell_web_client.h
index 4ab58d8c19eda24e63c26a79d7c9b3da36eed065..3c5743c2e6a539b41236d48cfeae480ca5b41555 100644
--- a/ios/web/shell/shell_web_client.h
+++ b/ios/web/shell/shell_web_client.h
@@ -21,7 +21,7 @@ class ShellWebClient : public WebClient {
   ~ShellWebClient() override;
 
   // WebClient implementation.
-  WebMainParts* CreateWebMainParts() override;
+  std::unique_ptr<web::WebMainParts> CreateWebMainParts() override;
   std::string GetProduct() const override;
   std::string GetUserAgent(bool desktop_user_agent) const override;
   void AllowCertificateError(
@@ -35,7 +35,7 @@ class ShellWebClient : public WebClient {
   ShellBrowserState* browser_state() const;
 
  private:
-  std::unique_ptr<ShellWebMainParts> web_main_parts_;
+  ShellWebMainParts* web_main_parts_;
 
   DISALLOW_COPY_AND_ASSIGN(ShellWebClient);
 };