Set up a field trial flag to prerender Instant search base url on omnibox focus event.

chrome/browser/ui/omnibox/omnibox_edit_model.cc

 // Copyright 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/ui/omnibox/omnibox_edit_model.h"
 
 #include <string>
 
 #include "base/auto_reset.h"
 #include "base/format_macros.h"
@@ skipping 926 matching lines @@
   if (delegate_->CurrentPageExists() && !user_input_in_progress_) {
     // TODO(jered): We may want to merge this into Start() and just call that
     // here rather than having a special entry point for zero-suggest.  Note
     // that we avoid PermanentURL() here because it's not guaranteed to give us
     // the actual underlying current URL, e.g. if we're on the NTP and the
     // |permanent_text_| is empty.
     autocomplete_controller()->StartZeroSuggest(AutocompleteInput(
         permanent_text_, base::string16::npos, base::string16(),
         delegate_->GetURL(), ClassifyPage(), false, false, true, true));
   }
+  // Prerender instant search base page.
+  if (chrome::ShouldPrerenderInstantSearchBaseOnFocus() &&
+      InstantSearchPrerenderer::GetForProfile(profile_))
+    delegate_->DoPrerender(AutocompleteMatch());

[kmadhusu, 2014/06/12 21:12:38]

We should not pass an new AutocompleteMatch() here. It makes me think may be
there is a better place to init InstantSearchPrerenderer. Can we do the
initialization in OmniboxCurrentPageDelegateImpl::OnFocusChanged()?

[sidharthms, 2014/06/12 23:33:34]

Moved to separate cl

 
   if (user_input_in_progress_ || !in_revert_)
     delegate_->OnInputStateChanged();
 }
 
 void OmniboxEditModel::SetCaretVisibility(bool visible) {
   // Caret visibility only matters if the omnibox has focus.
   if (focus_state_ != OMNIBOX_FOCUS_NONE) {
     SetFocusState(visible ? OMNIBOX_FOCUS_VISIBLE : OMNIBOX_FOCUS_INVISIBLE,
                   OMNIBOX_FOCUS_CHANGE_EXPLICIT);
@@ skipping 510 matching lines @@
   // Update state and notify view if the omnibox has focus and the caret
   // visibility changed.
   const bool was_caret_visible = is_caret_visible();
   focus_state_ = state;
   if (focus_state_ != OMNIBOX_FOCUS_NONE &&
       is_caret_visible() != was_caret_visible)
     view_->ApplyCaretVisibility();
 
   delegate_->OnFocusChanged(focus_state_, reason);
 }