Replace PruneAllButActive with PruneAllButVisible.

chrome/browser/ui/search/instant_controller.cc

Index: chrome/browser/ui/search/instant_controller.cc
diff --git a/chrome/browser/ui/search/instant_controller.cc b/chrome/browser/ui/search/instant_controller.cc
index 54f27f664854b9b867b8065be1bdf0dc34fa9b83..c5dc9a22692b058050ac26408fdf0341fd785307 100644
--- a/chrome/browser/ui/search/instant_controller.cc
+++ b/chrome/browser/ui/search/instant_controller.cc
@@ -825,7 +825,11 @@ bool InstantController::CommitIfPossible(InstantCommitType type) {
     overlay_->Submit(last_omnibox_text_);
   }
 
+  // Make sure the overlay WebContents is in a valid state (i.e., has a last
+  // committed entry, no transient entry, and no existing pending entry).
   scoped_ptr<content::WebContents> overlay = overlay_->ReleaseContents();
+  if (!overlay || !overlay->GetController().CanPruneAllButVisible())
+    return false;
 
   // If the overlay page has navigated since the last Update(), we need to add
   // the navigation to history ourselves. Else, the page will navigate after
@@ -865,12 +869,12 @@ bool InstantController::CommitIfPossible(InstantCommitType type) {
   }
 
   if (type == INSTANT_COMMIT_PRESSED_ALT_ENTER) {
-    overlay->GetController().PruneAllButActive();
+    CHECK(overlay->GetController().PruneAllButVisible());
   } else {
     content::WebContents* active_tab = browser_->GetActiveWebContents();
     AddSessionStorageHistogram(extended_enabled_, active_tab, overlay.get());
-    overlay->GetController().CopyStateFromAndPrune(
-        &active_tab->GetController());
+    CHECK(overlay->GetController().CopyStateFromAndPrune(
+              &active_tab->GetController()));
   }
 
   if (extended_enabled_) {