Implemented smooth scrolling using xinput2 in X11.

content/browser/web_contents/web_contents_impl.cc

Index: content/browser/web_contents/web_contents_impl.cc
diff --git a/content/browser/web_contents/web_contents_impl.cc b/content/browser/web_contents/web_contents_impl.cc
index c36e3a7772a42c2db4136b046e7e05f35b378305..85c189550575dd819ffd0a3f5c02daf84fc0617a 100644
--- a/content/browser/web_contents/web_contents_impl.cc
+++ b/content/browser/web_contents/web_contents_impl.cc
@@ -1591,7 +1591,14 @@ bool WebContentsImpl::HandleWheelEvent(
   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