Don't set the scroll styles (WS_VSCROLL and WS_HSCROLL) for WS_POPUP windows.

ui/views/win/hwnd_message_handler.cc

Index: ui/views/win/hwnd_message_handler.cc
===================================================================
--- ui/views/win/hwnd_message_handler.cc	(revision 244605)
+++ ui/views/win/hwnd_message_handler.cc	(working copy)
@@ -315,6 +315,18 @@
   }
 }
 
+void HideWindowsScrollBar(HWND window) {
+  ShowScrollBar(window, SB_BOTH, FALSE);
+  // Hiding the scrollbar also removes the WS_VSCROLL and WS_HSCROLL styles.
+  // We need to add the styles back to ensure that some trackpoint drivers
+  // which rely on them for scrolling work. However as this function can get
+  // called in the context of WM_SIZE we don't want to do this synchronously
+  // as that may trigger a WM_SIZE in some cases.
+  base::MessageLoop::current()->PostTask(
+      FROM_HERE,
+      base::Bind(&AddScrollStylesToWindow, window));
+}
+
 }  // namespace
 
 // A scoping class that prevents a window from being able to redraw in response
@@ -407,7 +419,8 @@
       menu_depth_(0),
       autohide_factory_(this),
       id_generator_(0),
-      scroll_styles_set_(false) {
+      needs_scroll_styles_(false),
+      size_move_loop_(false) {
 }
 
 HWNDMessageHandler::~HWNDMessageHandler() {
@@ -424,6 +437,27 @@
 
   // Create the window.
   WindowImpl::Init(parent, bounds);
+
+#if defined(USE_AURA)
+  // Certain trackpad drivers on Windows have bugs where in they don't generate
+  // WM_MOUSEWHEEL messages for the trackpoint and trackpad scrolling gestures
+  // unless there is an entry for Chrome with the class name of the Window.
+  // These drivers check if the window under the trackpoint has the WS_VSCROLL/
+  // WS_HSCROLL style and if yes they generate the legacy WM_VSCROLL/WM_HSCROLL
+  // messages. We add these styles to ensure that trackpad/trackpoint scrolling
+  // work.
+  // TODO(ananta)
+  // Look into moving the WS_VSCROLL and WS_HSCROLL style setting logic to the
+  // CalculateWindowStylesFromInitParams function. Doing it there seems to
+  // cause some interactive tests to fail. Investigation needed.
+  if (IsTopLevelWindow(hwnd())) {
+    long current_style = ::GetWindowLong(hwnd(), GWL_STYLE);
+    if (!(current_style & WS_POPUP)) {
+      AddScrollStylesToWindow(hwnd());
+      needs_scroll_styles_ = true;
+    }
+  }
+#endif
 }
 
 void HWNDMessageHandler::InitModalType(ui::ModalType modal_type) {
@@ -1366,25 +1400,6 @@
 
   delegate_->HandleCreate();
 
-#if defined(USE_AURA)
-  // Certain trackpad drivers on Windows have bugs where in they don't generate
-  // WM_MOUSEWHEEL messages for the trackpoint and trackpad scrolling gestures
-  // unless there is an entry for Chrome with the class name of the Window.
-  // These drivers check if the window under the trackpoint has the WS_VSCROLL/
-  // WS_HSCROLL style and if yes they generate the legacy WM_VSCROLL/WM_HSCROLL
-  // messages. We add these styles to ensure that trackpad/trackpoint scrolling
-  // work.
-  // TODO(ananta)
-  // Look into moving the WS_VSCROLL and WS_HSCROLL style setting logic to the
-  // CalculateWindowStylesFromInitParams function. Doing it there seems to
-  // cause some interactive tests to fail. Investigation needed.
-  if (IsTopLevelWindow(hwnd())) {
-    long current_style = ::GetWindowLong(hwnd(), GWL_STYLE);
-    ::SetWindowLong(hwnd(), GWL_STYLE,
-                    current_style | WS_VSCROLL | WS_HSCROLL);
-    scroll_styles_set_ = true;
-  }
-#endif
   // TODO(beng): move more of NWW::OnCreate here.
   return 0;
 }
@@ -1416,6 +1431,7 @@
 }
 
 void HWNDMessageHandler::OnEnterSizeMove() {
+  size_move_loop_ = true;
   delegate_->HandleBeginWMSizeMove();
   SetMsgHandled(FALSE);
 }
@@ -1434,6 +1450,11 @@
 void HWNDMessageHandler::OnExitSizeMove() {
   delegate_->HandleEndWMSizeMove();
   SetMsgHandled(FALSE);
+  size_move_loop_ = false;
+  // Please refer to the notes in the OnSize function for information about
+  // the scrolling hack.
+  if (needs_scroll_styles_)
+    HideWindowsScrollBar(hwnd());
 }
 
 void HWNDMessageHandler::OnGetMinMaxInfo(MINMAXINFO* minmax_info) {
@@ -2101,13 +2122,11 @@
   // We want the style to be present on the window. However we don't want
   // Windows to draw the scrollbars. To achieve this we hide the scroll bars
   // and readd them to the window style in a posted task which works.
-  if (scroll_styles_set_) {
-    ShowScrollBar(hwnd(), SB_BOTH, FALSE);
-    base::MessageLoop::current()->PostTask(
-        FROM_HERE,
-        base::Bind(&AddScrollStylesToWindow, hwnd()));
+  // If we are in the context of a size loop operation, we do this when the
+  // sizing operation completes.
+  if (needs_scroll_styles_ && !size_move_loop_)
+    HideWindowsScrollBar(hwnd());
 #endif
-  }
 }
 
 void HWNDMessageHandler::OnSysCommand(UINT notification_code,