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 f3750445bbd275209feeefb19aff0fb50340b144..494e142879a7628ac6336fea6a86ea3cd98e41f6 100644
--- a/chrome/browser/ui/search/instant_controller.cc
+++ b/chrome/browser/ui/search/instant_controller.cc
@@ -854,7 +854,11 @@ 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
@@ -894,12 +898,12 @@ 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()) {