Scrolling through tabs by using mouse-wheel on tab bar

chrome/browser/views/tabs/tab_strip.cc

Index: chrome/browser/views/tabs/tab_strip.cc
===================================================================
--- chrome/browser/views/tabs/tab_strip.cc	(revision 2596)
+++ chrome/browser/views/tabs/tab_strip.cc	(working copy)
@@ -442,7 +442,7 @@
 
   // Overridden from AnimationDelegate:
   virtual void AnimationEnded(const Animation* animation) {
-    tabstrip_->resize_layout_scheduled_ = false;
+    tabstrip_->needs_resize_layout_ = false;
     TabStrip::TabAnimation::AnimationEnded(animation);
   }
 
@@ -487,7 +487,7 @@
     : model_(model),
       resize_layout_factory_(this),
       added_as_message_loop_observer_(false),
-      resize_layout_scheduled_(false),
+      needs_resize_layout_(false),
       current_unselected_width_(Tab::GetStandardSize().width()),
       current_selected_width_(Tab::GetStandardSize().width()),
       available_width_for_tabs_(-1) {
@@ -869,7 +869,7 @@
     // We have "tiny tabs" if the tabs are so tiny that the unselected ones are
     // a different size to the selected ones.
     bool tiny_tabs = current_unselected_width_ != current_selected_width_;
-    if (!IsAnimating() && (!resize_layout_scheduled_ || tiny_tabs)) {
+    if (!IsAnimating() && (!needs_resize_layout_ || tiny_tabs)) {
       Layout();
     } else {
       SchedulePaint();
@@ -947,8 +947,7 @@
     // Tabs are not resized until a later time (when the mouse pointer leaves
     // the TabStrip).
     available_width_for_tabs_ = GetAvailableWidthForTabs(last_tab);
-    resize_layout_scheduled_ = true;
-    AddMessageLoopObserver();
+    needs_resize_layout_ = true;
     model_->CloseTabContentsAt(tab_index);
   }
 }
@@ -1053,34 +1052,36 @@
 }
 
 void TabStrip::DidProcessMessage(const MSG& msg) {
-  // We spy on three different Windows messages here to see if the mouse has
-  // moved out of the bounds of the tabstrip, which we use as our cue to kick
-  // of the resize animation. The messages are:
-  //
-  // WM_MOUSEMOVE:
-  //   For when the mouse moves from the tabstrip over into the rest of the
-  //   browser UI, i.e. within the bounds of the same windows HWND.
-  // WM_MOUSELEAVE:
-  //   For when the mouse moves very rapidly from a tab closed in the middle of
-  //   the tabstrip (_not_ the end) out of the bounds of the browser's HWND and
-  //   over some other HWND.
-  // WM_NCMOUSELEAVE:
-  //   For when the mouse moves very rapidly from the end of the tabstrip (when
-  //   the last tab is closed and the mouse is left floating over the title
-  //   bar). Because the empty area of the tabstrip at the end of the title bar
-  //   is registered by the ChromeFrame as part of the "caption" area of the
-  //   window (the frame's OnNCHitTest method returns HTCAPTION for this
-  //   region), the frame's HWND receives a WM_MOUSEMOVE message immediately,
-  //   because as far as it is concerned the mouse has _left_ the client area
-  //   of the window (and is now over the non-client area). To be notified
-  //   again when the mouse leaves the _non-client_ area, we use the
-  //   WM_NCMOUSELEAVE message, which causes us to re-evaluate the cursor
-  //   position and correctly resize the tabstrip.
-  //
   switch (msg.message) {
+    // We spy on three different Windows messages here to see if the mouse has
+    // moved out of the bounds of the tabstrip, which we use as our cue to kick
+    // of the resize animation. The messages are:
+    //
+    // WM_MOUSEMOVE:
+    //   For when the mouse moves from the tabstrip over into the rest of the
+    //   browser UI, i.e. within the bounds of the same windows HWND.
+    // WM_MOUSELEAVE:
+    //   For when the mouse moves very rapidly from a tab closed in the middle
+    //   of the tabstrip (_not_ the end) out of the bounds of the browser's
+    //   HWND and over some other HWND.
+    // WM_NCMOUSELEAVE:
+    //   For when the mouse moves very rapidly from the end of the tabstrip
+    //   (when the last tab is closed and the mouse is left floating over the
+    //   title bar). Because the empty area of the tabstrip at the end of the
+    //   title bar is registered by the ChromeFrame as part of the "caption"
+    //   area of the window (the frame's OnNCHitTest method returns HTCAPTION
+    //   for this region), the frame's HWND receives a WM_MOUSEMOVE message
+    //   immediately, because as far as it is concerned the mouse has _left_
+    //   the client area of the window (and is now over the non-client area).
+    //   To be notified again when the mouse leaves the _non-client_ area, we
+    //   use the WM_NCMOUSELEAVE message, which causes us to re-evaluate the
+    //   cursor position and correctly resize the tabstrip.
+    //
     case WM_MOUSEMOVE:
     case WM_MOUSELEAVE:
     case WM_NCMOUSELEAVE:
+      if (!needs_resize_layout_)
+        break;
       if (!IsCursorInTabStripZone()) {
         // Mouse moved outside the tab slop zone, start a timer to do a resize
         // layout after a short while...
@@ -1097,6 +1098,20 @@
         resize_layout_factory_.RevokeAll();
       }
       break;
+    // We also watch out for mouse-wheel messages here to allow the user to
+    // leaf through the tabs by scrolling while the mouse cursor is in the tab
+    // strip zone.
+    case WM_MOUSEWHEEL:
+      if (!IsCursorInTabStripZone())
+        break;
+      CHECK(model_);
+      // A positive value indicates that the wheel was rotated away from the
+      // user; a negative value indicates rotation toward the user.
+      if (GET_WHEEL_DELTA_WPARAM(msg.wParam) > 0)
+        model_->SelectPreviousTab();
+      else
+        model_->SelectNextTab();
+      break;
   }
 }
 
@@ -1129,6 +1144,8 @@
     drop_indicator_width = drop_image->width();
     drop_indicator_height = drop_image->height();
   }
+
+  AddMessageLoopObserver();
 }
 
 Tab* TabStrip::GetTabAt(int index) const {
@@ -1224,10 +1241,6 @@
 void TabStrip::ResizeLayoutTabs() {
   resize_layout_factory_.RevokeAll();
 
-  // It is critically important that this is unhooked here, otherwise we will
-  // keep spying on messages forever.
-  RemoveMessageLoopObserver();
-
   available_width_for_tabs_ = -1;
   double unselected, selected;
   GetDesiredTabWidths(GetTabCount(), &unselected, &selected);
@@ -1461,7 +1474,7 @@
 void TabStrip::LayoutNewTabButton(double last_tab_right,
                                   double unselected_width) {
   int delta = abs(Round(unselected_width) - Tab::GetStandardSize().width());
-  if (delta > 1 && !resize_layout_scheduled_) {
+  if (delta > 1 && !needs_resize_layout_) {
     // We're shrinking tabs, so we need to anchor the New Tab button to the
     // right edge of the TabStrip's bounds, rather than the right edge of the
     // right-most Tab, otherwise it'll bounce when animating.