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 d6b0d4101fbb7925452af2bea314f89d960f7953..daec2d31c313cbcffc27b22a36458ecc8ddc63c4 100644
--- a/chrome/browser/ui/startup/startup_browser_creator_impl.cc
+++ b/chrome/browser/ui/startup/startup_browser_creator_impl.cc
@@ -97,6 +97,8 @@
 
 #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 +808,20 @@ Browser* StartupBrowserCreatorImpl::OpenTabsInBrowser(Browser* browser,
 #endif
   }
 
+#if defined(USE_ASH)
+  if (ash::Shell::HasInstance()) {
+    // 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);