Made page zoom handling work with smooth scroll devices

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 88f58a782fd7544ae316343b06dc0b6dd50546c2..a0c4db77d66823ba80fdd472f5f768d940b666d8 100644
--- a/content/browser/web_contents/web_contents_impl.cc
+++ b/content/browser/web_contents/web_contents_impl.cc
@@ -396,6 +396,7 @@ WebContentsImpl::WebContentsImpl(BrowserContext* browser_context)
       closed_by_user_gesture_(false),
       minimum_zoom_percent_(static_cast<int>(kMinimumZoomFactor * 100)),
       maximum_zoom_percent_(static_cast<int>(kMaximumZoomFactor * 100)),
+      zoom_scroll_amount_(0),
       render_view_message_source_(NULL),
       render_frame_message_source_(NULL),
       fullscreen_widget_routing_id_(MSG_ROUTING_NONE),
@@ -1587,7 +1588,14 @@ 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_);

[Avi (use Gerrit), 2016/01/05 01:46:24]

Let's make it C++, so do std::lround, since we're returning to an integer value.

Also, include <cmath> as that's where it's defined.

[Will Shackleton, 2016/01/05 21:50:05]

Done.

+    zoom_scroll_amount_ -= whole_zoom_scroll_amount;
+    if (whole_zoom_scroll_amount != 0) {
+      delegate_->ContentsZoomChange(whole_zoom_scroll_amount > 0);
+    }
     return true;
   }
 #endif