Replace PruneAllButActive with PruneAllButVisible.

chrome/browser/prerender/prerender_manager.cc

Index: chrome/browser/prerender/prerender_manager.cc
diff --git a/chrome/browser/prerender/prerender_manager.cc b/chrome/browser/prerender/prerender_manager.cc
index dc1f78006fdc69b5eaa1c6942eea181cec7ef8e9..7e63ec7ea5fadd6e038fce6fdcb4604d0928a7aa 100644
--- a/chrome/browser/prerender/prerender_manager.cc
+++ b/chrome/browser/prerender/prerender_manager.cc
@@ -427,6 +427,14 @@ bool PrerenderManager::MaybeUsePrerenderedPage(WebContents* web_contents,
       prerender_data->contents()->prerender_contents()) {
     if (web_contents == new_web_contents)
       return false;  // Do not swap in to ourself.
+
+    // We cannot swap in if there is no last committed entry, because we would
+    // show a blank page under an existing entry from the current tab.  Even if
+    // there is a pending entry, it may not commit.
+    // TODO(creis): If there is a pending navigation and no last committed
+    // entry, we might be able to transfer the network request instead.
+    if (!new_web_contents->GetController().CanPruneAllButVisible())
+      return false;
   }
 
   // Do not use the prerendered version if there is an opener object.
@@ -520,8 +528,8 @@ bool PrerenderManager::MaybeUsePrerenderedPage(WebContents* web_contents,
   MarkWebContentsAsPrerendered(new_web_contents, prerender_contents->origin());
 
   // Merge the browsing history.
-  new_web_contents->GetController().CopyStateFromAndPrune(
-      &old_web_contents->GetController());
+  CHECK(new_web_contents->GetController().CopyStateFromAndPrune(
+            &old_web_contents->GetController()));
   CoreTabHelper::FromWebContents(old_web_contents)->delegate()->
       SwapTabContents(old_web_contents, new_web_contents);
   prerender_contents->CommitHistory(new_web_contents);