Add TopSites::GetTemporaryThumbnailScore().

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 6acae584d0b1ad475803379470fa797730581c04..ac02e1f59d01236db5bd012cace4033ebb884fb5 100644
--- a/chrome/browser/tab_contents/thumbnail_generator.cc
+++ b/chrome/browser/tab_contents/thumbnail_generator.cc
@@ -671,13 +671,13 @@ bool ThumbnailGenerator::ShouldUpdateThumbnail(Profile* profile,
   if (!HistoryService::CanAddURL(url))
     return false;
   // Skip if the top sites list is full, and the URL is not known.
-  const bool is_known = top_sites->IsKnownURL(url);
-  if (top_sites->IsFull() && !is_known)
+  if (top_sites->IsFull() && !top_sites->IsKnownURL(url))
     return false;
-  // Skip if we don't have to udpate the existing thumbnail.
+  // Skip if we don't have to udpate the existing thumbnail. Note that an
+  // unknown URL can have a thumbnail score. This can happen if a
+  // thumbnail is set but not yet saved.
   ThumbnailScore current_score;
-  if (is_known &&
-      top_sites->GetPageThumbnailScore(url, &current_score) &&
+  if (top_sites->GetPageThumbnailScore(url, &current_score) &&
       !current_score.ShouldConsiderUpdating())
     return false;