Have SearchProvider look up the omnibox start margin directly.

chrome/browser/autocomplete/search_provider.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/autocomplete/search_provider.h"
 
 #include <algorithm>
 #include <cmath>
 
 #include "base/callback.h"
@@ skipping 18 matching lines @@
 #include "chrome/browser/history/history_service_factory.h"
 #include "chrome/browser/history/in_memory_database.h"
 #include "chrome/browser/metrics/variations/variations_http_header_provider.h"
 #include "chrome/browser/omnibox/omnibox_field_trial.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/search/search.h"
 #include "chrome/browser/search_engines/search_engine_type.h"
 #include "chrome/browser/search_engines/template_url_prepopulate_data.h"
 #include "chrome/browser/search_engines/template_url_service.h"
 #include "chrome/browser/search_engines/template_url_service_factory.h"
+#include "chrome/browser/ui/browser.h"
+#include "chrome/browser/ui/browser_finder.h"
+#include "chrome/browser/ui/browser_instant_controller.h"
+#include "chrome/browser/ui/search/instant_controller.h"
 #include "chrome/common/net/url_fixer_upper.h"
 #include "chrome/common/pref_names.h"
 #include "chrome/common/url_constants.h"
 #include "grit/generated_resources.h"
 #include "net/base/escape.h"
 #include "net/base/load_flags.h"
 #include "net/base/net_util.h"
 #include "net/http/http_request_headers.h"
 #include "net/http/http_response_headers.h"
 #include "net/url_request/url_fetcher.h"
@@ skipping 194 matching lines @@
 const char SearchProvider::kTrue[] = "true";
 const char SearchProvider::kFalse[] = "false";
 
 SearchProvider::SearchProvider(AutocompleteProviderListener* listener,
                                Profile* profile)
     : AutocompleteProvider(listener, profile,
           AutocompleteProvider::TYPE_SEARCH),
       providers_(TemplateURLServiceFactory::GetForProfile(profile)),
       suggest_results_pending_(0),
       field_trial_triggered_(false),
-      field_trial_triggered_in_session_(false),
-      omnibox_start_margin_(-1) {
+      field_trial_triggered_in_session_(false) {
 }
 
 // static
 AutocompleteMatch SearchProvider::CreateSearchSuggestion(
     AutocompleteProvider* autocomplete_provider,
     int relevance,
     AutocompleteMatch::Type type,
     const TemplateURL* template_url,
     const string16& query_string,
     const string16& input_text,
@@ skipping 97 matching lines @@
       new_entry.mutable_field_trial_triggered_in_session()->Add(
           field_trial_hashes[i]);
     }
   }
 }
 
 void SearchProvider::ResetSession() {
   field_trial_triggered_in_session_ = false;
 }
 
-void SearchProvider::SetOmniboxStartMargin(int omnibox_start_margin) {
-  omnibox_start_margin_ = omnibox_start_margin;
-}
-
 SearchProvider::~SearchProvider() {
 }
 
 // static
 void SearchProvider::RemoveStaleResults(const string16& input,
                                         int verbatim_relevance,
                                         SuggestResults* suggest_results,
                                         NavigationResults* navigation_results) {
   DCHECK_GE(verbatim_relevance, 0);
   // Keep pointers to the head of (the highest scoring elements of)
@@ skipping 989 matching lines @@
 }
 
 void SearchProvider::AddMatchToMap(const string16& query_string,
                                    const string16& input_text,
                                    int relevance,
                                    bool relevance_from_server,
                                    AutocompleteMatch::Type type,
                                    int accepted_suggestion,
                                    bool is_keyword,
                                    MatchMap* map) {
+  int omnibox_start_margin = chrome::kDisableStartMargin;
+// browser_finder does not exist for Android. On IOS, start margin is not used.

[Peter Kasting, 2013/08/09 21:03:46]

Nit: To avoid unusual comment indenting, how about:

  // On non-mobile, ask the instant controller for the appropriate start margin.
  // On Android, FindBrowserWithProfile() doesn't exist, and on iOS, the start
  // margin is unused, so leave the value as default there.
  int omnibox_start_margin = chrome::kDisableStartMargin;
#if ...

You can simplify this comment if we don't use the start margin on Android
anyway, by just saying that this is unused on mobile.

[jeremycho, 2013/08/09 23:55:09]

Done.

+#if !defined(OS_ANDROID) && !defined(IOS)
+  if (chrome::IsInstantExtendedAPIEnabled()) {
+    Browser* browser =
+        chrome::FindBrowserWithProfile(profile_, chrome::GetActiveDesktop());
+    if (browser && browser->instant_controller() &&
+        browser->instant_controller()->instant()) {
+      omnibox_start_margin =
+          browser->instant_controller()->instant()->omnibox_bounds().x();
+    }
+  }
+#endif  // !defined(OS_ANDROID) && !defined(IOS)
+
   const TemplateURL* template_url = is_keyword ?
       providers_.GetKeywordProviderURL() : providers_.GetDefaultProviderURL();
   AutocompleteMatch match = CreateSearchSuggestion(this, relevance, type,
       template_url, query_string, input_text, input_, is_keyword,
-      accepted_suggestion, omnibox_start_margin_,
+      accepted_suggestion, omnibox_start_margin,
       !is_keyword || providers_.default_provider().empty());
   if (!match.destination_url.is_valid())
     return;
   match.RecordAdditionalInfo(kRelevanceFromServerKey,
                              relevance_from_server ? kTrue : kFalse);
 
   // Try to add |match| to |map|.  If a match for |query_string| is already in
   // |map|, replace it if |match| is more relevant.
   // NOTE: Keep this ToLower() call in sync with url_database.cc.
   const std::pair<MatchMap::iterator, bool> i(
@@ skipping 116 matching lines @@
     it->set_relevance(max_query_relevance);
     it->set_relevance_from_server(relevance_from_server);
   }
 }
 
 void SearchProvider::UpdateDone() {
   // We're done when the timer isn't running, there are no suggest queries
   // pending, and we're not waiting on Instant.
   done_ = !timer_.IsRunning() && (suggest_results_pending_ == 0);
 }