Return unique_ptr from WebClient::CreateWebMainParts()

ios/chrome/browser/web/chrome_web_client.mm

Index: ios/chrome/browser/web/chrome_web_client.mm
diff --git a/ios/chrome/browser/web/chrome_web_client.mm b/ios/chrome/browser/web/chrome_web_client.mm
index ccf042f332e166d5afd3775ff80fd8170d17cb16..2e3f031e47fd547a584931081e291475c8ccbbf9 100644
--- a/ios/chrome/browser/web/chrome_web_client.mm
+++ b/ios/chrome/browser/web/chrome_web_client.mm
@@ -8,6 +8,7 @@
 #include "base/files/file_util.h"
 #include "base/ios/ios_util.h"
 #include "base/mac/bundle_locations.h"
+#include "base/memory/ptr_util.h"
 #include "base/strings/sys_string_conversions.h"
 #include "components/dom_distiller/core/url_constants.h"
 #include "components/prefs/pref_service.h"
@@ -59,8 +60,9 @@ ChromeWebClient::ChromeWebClient() {}
 
 ChromeWebClient::~ChromeWebClient() {}
 
-web::WebMainParts* ChromeWebClient::CreateWebMainParts() {
-  return new IOSChromeMainParts(*base::CommandLine::ForCurrentProcess());
+std::unique_ptr<web::WebMainParts> ChromeWebClient::CreateWebMainParts() {
+  return base::MakeUnique<IOSChromeMainParts>(
+      *base::CommandLine::ForCurrentProcess());
 }
 
 void ChromeWebClient::PreWebViewCreation() const {