Fix for out-of-sync scale factor issue

chrome/browser/ui/startup/startup_browser_creator_impl.cc

Index: chrome/browser/ui/startup/startup_browser_creator_impl.cc
diff --git a/chrome/browser/ui/startup/startup_browser_creator_impl.cc b/chrome/browser/ui/startup/startup_browser_creator_impl.cc
index 451b0e5c5b8b01fc7719ceb7a846a9a56cd9f499..d1ad58f7e4e82ec72f866bece9e63f95c3663de1 100644
--- a/chrome/browser/ui/startup/startup_browser_creator_impl.cc
+++ b/chrome/browser/ui/startup/startup_browser_creator_impl.cc
@@ -95,6 +95,8 @@
 
 #if defined(USE_ASH)
 #include "ash/launcher/launcher_types.h"
+#include "ash/shell.h"
+#include "ui/aura/window.h"
 #endif
 
 #if defined(OS_MACOSX)
@@ -806,6 +808,18 @@ Browser* StartupBrowserCreatorImpl::OpenTabsInBrowser(Browser* browser,
 #endif
   }
 
+#if defined(USE_ASH)
+  // Set the browser's root window to be an active root window now so
+  // that that web contents can determine correct scale factor for the
+  // renderer. This is a short term fix for crbug.com/155201.  Without
+  // this, the renderer may use wrong scale factor first, then
+  // switched to the correct scale factor, which can cause race
+  // condition and lead to the results rendered at wrong scale factor.
+  // Long term fix is tracked in crbug.com/15543.
+  ash::Shell::GetInstance()->set_active_root_window(
+      browser->window()->GetNativeWindow()->GetRootWindow());
+#endif
+
   // In kiosk mode, we want to always be fullscreen, so switch to that now.
   if (CommandLine::ForCurrentProcess()->HasSwitch(switches::kKioskMode))
     chrome::ToggleFullscreenMode(browser);