Fix prerender histograms for multiple prerender case.

chrome/browser/prerender/prerender_tab_helper.cc

Index: chrome/browser/prerender/prerender_tab_helper.cc
diff --git a/chrome/browser/prerender/prerender_tab_helper.cc b/chrome/browser/prerender/prerender_tab_helper.cc
index 5d4e011875093c4216b7ef5756798711a8f19157..e10b034627ddbdae209a5dddd4a090da12ffc0e2 100644
--- a/chrome/browser/prerender/prerender_tab_helper.cc
+++ b/chrome/browser/prerender/prerender_tab_helper.cc
@@ -90,8 +90,8 @@ class PrerenderTabHelper::PixelStats {
       PrerenderManager* prerender_manager =
           tab_helper_->MaybeGetPrerenderManager();
       if (prerender_manager) {
-        prerender_manager->histograms()->RecordFractionPixelsFinalAtSwapin(
-            CompareBitmaps(bitmap_.get(), bitmap.get()));
+        prerender_manager->RecordFractionPixelsFinalAtSwapin(
+            web_contents, CompareBitmaps(bitmap_.get(), bitmap.get()));
       }
       bitmap_.reset();
       bitmap_web_contents_ = NULL;
@@ -228,7 +228,7 @@ bool PrerenderTabHelper::IsPrerendered() {
   PrerenderManager* prerender_manager = MaybeGetPrerenderManager();
   if (!prerender_manager)
     return false;
-  return prerender_manager->IsWebContentsPrerendered(web_contents());
+  return prerender_manager->IsWebContentsPrerendered(web_contents(), NULL);
 }
 
 void PrerenderTabHelper::PrerenderSwappedIn() {
@@ -240,7 +240,7 @@ void PrerenderTabHelper::PrerenderSwappedIn() {
                                                   web_contents(), url_);
     PrerenderManager* prerender_manager = MaybeGetPrerenderManager();
     if (prerender_manager)
-      prerender_manager->histograms()->RecordFractionPixelsFinalAtSwapin(1.0);
+      prerender_manager->RecordFractionPixelsFinalAtSwapin(web_contents(), 1.0);
   } else {
     // If we have not finished loading yet, record the actual load start, and
     // rebase the start time to now.