Have SearchProvider look up the omnibox start margin directly.

chrome/browser/ui/search/instant_controller.h

Index: chrome/browser/ui/search/instant_controller.h
diff --git a/chrome/browser/ui/search/instant_controller.h b/chrome/browser/ui/search/instant_controller.h
index b204ba0239da0239c199fe425bfef95c3c4b2c70..adef778de9a13045bb138bb43f024ad80043eb8f 100644
--- a/chrome/browser/ui/search/instant_controller.h
+++ b/chrome/browser/ui/search/instant_controller.h
@@ -33,6 +33,10 @@ namespace content {
 class WebContents;
 }
 
+namespace gfx {
+class Rect;
+}
+
 // Macro used for logging debug events. |message| should be a std::string.
 #define LOG_INSTANT_DEBUG_EVENT(controller, message) \
     controller->LogDebugEvent(message)
@@ -55,6 +59,9 @@ class InstantController : public InstantPage::Delegate {
   // Sets the stored start-edge margin and width of the omnibox.
   void SetOmniboxBounds(const gfx::Rect& bounds);
 
+  // Gets the stored start-edge margin and width of the omnibox.
+  gfx::Rect GetOmniboxBounds();

[samarth, 2013/08/06 18:09:32]

Make this a simple accessor: omnibox_bounds()

[jeremycho, 2013/08/06 21:03:04]

Done.

+
   // Notifies |instant_Tab_| to toggle voice search.
   void ToggleVoiceSearch();