Implemented smooth scrolling using xinput2 in X11.

content/browser/web_contents/web_contents_impl.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/browser/web_contents/web_contents_impl.h"
 
 #include <utility>
 
 #include "base/command_line.h"
 #include "base/lazy_instance.h"
@@ skipping 1573 matching lines @@
 #if !defined(OS_MACOSX)
   // On platforms other than Mac, control+mousewheel may change zoom. On Mac,
   // this isn't done for two reasons:
   //   -the OS already has a gesture to do this through pinch-zoom
   //   -if a user starts an inertial scroll, let's go, and presses control
   //      (i.e. control+tab) then the OS's buffered scroll events will come in
   //      with control key set which isn't what the user wants
   if (delegate_ && event.wheelTicksY &&
       (event.modifiers & blink::WebInputEvent::ControlKey) &&
       !event.canScroll) {
-    delegate_->ContentsZoomChange(event.wheelTicksY > 0);
+    // Count only integer cumulative scrolls as zoom events; this handles
+    // smooth scroll and regular scroll device behavior.
+    zoom_scroll_amount_ += event.wheelTicksY;
+    int whole_zoom_scroll_amount = round(zoom_scroll_amount_);
+    zoom_scroll_amount_ -= whole_zoom_scroll_amount;
+    if (whole_zoom_scroll_amount != 0) {
+      delegate_->ContentsZoomChange(whole_zoom_scroll_amount > 0);
+    }
     return true;
   }
 #endif
   return false;
 }
 
 bool WebContentsImpl::PreHandleGestureEvent(
     const blink::WebGestureEvent& event) {
   return delegate_ && delegate_->PreHandleGestureEvent(this, event);
 }
@@ skipping 3198 matching lines @@
   return NULL;
 }
 
 void WebContentsImpl::SetForceDisableOverscrollContent(bool force_disable) {
   force_disable_overscroll_content_ = force_disable;
   if (view_)
     view_->SetOverscrollControllerEnabled(CanOverscrollContent());
 }
 
 }  // namespace content