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 e117a3a908034bbe58820fd82675b84df443c114..80e90e4a5eb631861a122076c8eb208b9a933881 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)
@@ -93,6 +97,11 @@ class InstantController : public InstantPage::Delegate {
     return debug_events_;
   }
 
+  // Gets the stored start-edge margin and width of the omnibox.
+  const gfx::Rect omnibox_bounds() {
+    return omnibox_bounds_;
+  }
+
   // Used by BrowserInstantController to notify InstantController about the
   // instant support change event for the active web contents.
   void InstantSupportChanged(InstantSupportState instant_support);