Prevent browser thumbnailer from trying to read from frontbuffer (surface texture) when none exists.

chrome/browser/tab_contents/thumbnail_generator.cc

Index: chrome/browser/tab_contents/thumbnail_generator.cc
diff --git a/chrome/browser/tab_contents/thumbnail_generator.cc b/chrome/browser/tab_contents/thumbnail_generator.cc
index 1834ae748f43b2c278159a99e2bbaa658389e92c..44fcdb752e2f4d525999e31f91973c97c1cca780 100644
--- a/chrome/browser/tab_contents/thumbnail_generator.cc
+++ b/chrome/browser/tab_contents/thumbnail_generator.cc
@@ -443,6 +443,11 @@ void ThumbnailGenerator::UpdateThumbnailIfNecessary(
   Profile* profile =
       Profile::FromBrowserContext(web_contents->GetBrowserContext());
   history::TopSites* top_sites = profile->GetTopSites();
+  bool surface_available =
+      web_contents->GetRenderWidgetHostView()->IsSurfaceAvailableForCopy();
+  // Skip if we can't update the thumbnail.
+  if (!surface_available)
+    return;
   // Skip if we don't need to update the thumbnail.
   if (!ShouldUpdateThumbnail(profile, top_sites, url))
     return;