Allow SiteInstance for about:blank in new tab to be reused.

content/browser/tab_contents/tab_contents.cc

Index: content/browser/tab_contents/tab_contents.cc
diff --git a/content/browser/tab_contents/tab_contents.cc b/content/browser/tab_contents/tab_contents.cc
index 3d952f96d195328f1eab9883a2d61ed3291ff828..a8c4bbe8771702bdb474d856f84948afe9391770 100644
--- a/content/browser/tab_contents/tab_contents.cc
+++ b/content/browser/tab_contents/tab_contents.cc
@@ -1751,9 +1751,13 @@ void TabContents::DidNavigate(RenderViewHost* rvh,
   if (content::PageTransitionIsMainFrame(params.transition))
     render_manager_.DidNavigateMainFrame(rvh);
 
-  // Update the site of the SiteInstance if it doesn't have one yet.
-  if (!static_cast<SiteInstanceImpl*>(GetSiteInstance())->HasSite())
+  // Update the site of the SiteInstance if it doesn't have one yet, unless
+  // this is for about:blank.  In that case, the SiteInstance can still be
+  // considered unused until a navigation to a real page.
+  if (!static_cast<SiteInstanceImpl*>(GetSiteInstance())->HasSite() &&
+      params.url != GURL(chrome::kAboutBlankURL)) {
     static_cast<SiteInstanceImpl*>(GetSiteInstance())->SetSite(params.url);
+  }
 
   // Need to update MIME type here because it's referred to in
   // UpdateNavigationCommands() called by RendererDidNavigate() to