alternate ntp: implement Show/HideBars API to reduce jank when showing/hiding bars

chrome/common/render_messages.h

Index: chrome/common/render_messages.h
diff --git a/chrome/common/render_messages.h b/chrome/common/render_messages.h
index bdc6bebd7c2af5e486b489e88561022d274ab829..7b420efe28fed9735d85f91e315e5fe634042132 100644
--- a/chrome/common/render_messages.h
+++ b/chrome/common/render_messages.h
@@ -312,6 +312,8 @@ IPC_MESSAGE_ROUTED2(ChromeViewMsg_SearchBoxMarginChange,
                     int /* start */,
                     int /* end */)
 
+IPC_MESSAGE_ROUTED0(ChromeViewMsg_SearchBoxBarsHidden)
+
 IPC_MESSAGE_ROUTED0(ChromeViewMsg_DetermineIfPageSupportsInstant)
 
 IPC_MESSAGE_ROUTED1(ChromeViewMsg_SearchBoxAutocompleteResults,
@@ -698,6 +700,14 @@ IPC_MESSAGE_ROUTED3(ChromeViewHostMsg_ShowInstantOverlay,
 IPC_MESSAGE_ROUTED1(ChromeViewHostMsg_FocusOmnibox,
                     int /* page_id */)
 
+// Sent by Instant to show any attached bars.
+IPC_MESSAGE_ROUTED1(ChromeViewHostMsg_SearchBoxShowBars,
+                    int /* page_id */)
+
+// Sent by Instant to hide any attached bars.
+IPC_MESSAGE_ROUTED1(ChromeViewHostMsg_SearchBoxHideBars,
+                    int /* page_id */)
+
 IPC_MESSAGE_ROUTED1(ChromeViewHostMsg_StartCapturingKeyStrokes,
                     int /* page_id */)