Make mouse wheel events trigger WebContentsObserver::DidGetUserInteraction.

content/browser/renderer_host/render_widget_host_impl.cc

Index: content/browser/renderer_host/render_widget_host_impl.cc
diff --git a/content/browser/renderer_host/render_widget_host_impl.cc b/content/browser/renderer_host/render_widget_host_impl.cc
index cc7def8580adc072b2a0119b72d1e6b8d12fdabf..4cb3afb692ae12f550e7ace3af79dba39e77c12f 100644
--- a/content/browser/renderer_host/render_widget_host_impl.cc
+++ b/content/browser/renderer_host/render_widget_host_impl.cc
@@ -92,6 +92,12 @@ using blink::WebTextDirection;
 namespace content {
 namespace {
 
+// The amount of time after a mouse wheel event is sent to the delegate
+// OnUserInteraction method before another mouse wheel event will be sent. Equal
+// to blink's EventHandler interval for detecting the end of a scroll event.
+const base::TimeDelta g_wheel_coalesce_interval =

[calamity, 2015/11/03 02:16:13]

nit: Consider kWheelCoalesceInterval if this is never changed.

[dominickn, 2015/11/03 21:29:42]

I'll leave this unless one of the content reviewers wants it.

[tdresser, 2015/11/03 21:39:48]

I think kWheelCoalesceInterval would be more standard.

[dominickn, 2015/11/04 00:18:31]

Done.

+    base::TimeDelta::FromMilliseconds(100);

[nasko, 2015/11/03 20:45:59]

What is the rationale for picking this number?

[dominickn, 2015/11/03 21:29:42]

It's the same value used by blink in its orthogonal heuristic to detect the end
of a scroll event (if no mouse wheel has been seen for 0.1 seconds, send end
scroll).

[nasko, 2015/11/04 17:31:22]

Please put this in a comment, so it is clear for people reading the code.

[dominickn, 2015/11/04 23:21:25]

Done, expanded the preceding comment.

+
 bool g_check_for_pending_resize_ack = true;
 
 // <process id, routing id>
@@ -204,6 +210,7 @@ RenderWidgetHostImpl::RenderWidgetHostImpl(RenderWidgetHostDelegate* delegate,
           base::TimeDelta::FromMilliseconds(kHungRendererDelayMs)),
       new_content_rendering_delay_(
           base::TimeDelta::FromMilliseconds(kNewContentRenderingDelayMs)),
+      wheel_coalesce_timer_(nullptr),

[nasko, 2015/11/03 20:45:59]

scoped_ptr is default initialized to nullptr, so no need for explicit
initialization here.

[dominickn, 2015/11/03 21:29:42]

Done.

       weak_factory_(this) {
   CHECK(delegate_);
   CHECK_NE(MSG_ROUTING_NONE, routing_id_);
@@ -1860,6 +1867,12 @@ InputEventAckState RenderWidgetHostImpl::FilterInputEvent(
         event.type == WebInputEvent::GestureTapDown ||
         event.type == WebInputEvent::RawKeyDown) {
       delegate_->OnUserInteraction(event.type);
+    } else if (event.type == WebInputEvent::MouseWheel) {
+      if (!wheel_coalesce_timer_.get() ||
+          wheel_coalesce_timer_->Elapsed() > g_wheel_coalesce_interval) {
+        delegate_->OnUserInteraction(event.type);
+      }
+      wheel_coalesce_timer_.reset(new base::ElapsedTimer());

[nasko, 2015/11/03 20:45:59]

If the timer will always be reset to something, why not initialize it to a valid
value in the constructor? This will allow you to drop the check for existence in
the if statement above and make it trivial to read.

[dominickn, 2015/11/03 21:29:42]

Done.

     }
   }