Pipe "is pinned to left/right", "has horizontal/vertical scrollbar",

content/common/view_messages.h

Index: content/common/view_messages.h
diff --git a/content/common/view_messages.h b/content/common/view_messages.h
index eca2d1a463635a87313cfbd7e5ca1f8cc7edce66..964579f44436ac884b85bc0bbf33959830502e73 100644
--- a/content/common/view_messages.h
+++ b/content/common/view_messages.h
@@ -1662,6 +1662,20 @@ IPC_MESSAGE_ROUTED3(ViewHostMsg_OpenURL,
 IPC_MESSAGE_ROUTED1(ViewHostMsg_DidContentsPreferredSizeChange,
                     gfx::Size /* pref_size */)
 
+// Notifies that the scrollbars-visible state of the content changed.
+IPC_MESSAGE_ROUTED2(ViewHostMsg_DidChangeScrollOffsetPinningForMainFrame,
+                    bool /* has_horizontal_scrollbar */,
+                    bool /* has_vertical_scrollbar */)
+
+// Notifies that the pinned-to-side state of the content changed.
+IPC_MESSAGE_ROUTED2(ViewHostMsg_DidChangeScrollbarsForMainFrame,
+                    bool /* pinned_to_left */,
+                    bool /* pinned_to_right */)
+
+// Notifies that the number of JavaScript scroll handlers changed.
+IPC_MESSAGE_ROUTED1(ViewHostMsg_DidChangeNumWheelEvents,
+                    int /* count */)
+
 // A message from HTML-based UI.  When (trusted) Javascript calls
 // send(message, args), this message is sent to the browser.
 IPC_MESSAGE_ROUTED3(ViewHostMsg_WebUISend,