Wheel scroll latching enabled behind flag.

content/browser/renderer_host/input/mouse_wheel_event_queue.h

Index: content/browser/renderer_host/input/mouse_wheel_event_queue.h
diff --git a/content/browser/renderer_host/input/mouse_wheel_event_queue.h b/content/browser/renderer_host/input/mouse_wheel_event_queue.h
index a2722310b74b68c0c7e5c3f261851c65a969432d..161dfbb0aab8bf59443219e0ebc5ecfa8e3b26b8 100644
--- a/content/browser/renderer_host/input/mouse_wheel_event_queue.h
+++ b/content/browser/renderer_host/input/mouse_wheel_event_queue.h
@@ -19,7 +19,8 @@ namespace content {
 // ScrollUpdate was sent for wheel based gesture scrolls.
 // Set the default wheel transaction to 0ms until
 // crbug.com/526463 is fully implemented.
-const int64_t kDefaultWheelScrollTransactionMs = 0;  // 100;
+const int64_t kDefaultWheelScrollTransactionMs = 0;
+const int64_t kDefaultWheelScrollLatchingTransactionMs = 100;

[tdresser, 2016/07/22 15:43:15]

What's the difference between these constants? Why do we need a transaction time
for Mac?

[sahel, 2016/07/25 15:54:53]

This is for handling the cases that phase info is not available. e.g. Wheel
scroll events On Mac.
Maybe I should change the title of the patch, so that it represents both
latching cases.

[tdresser, 2016/07/25 16:46:55]

We don't need a timeout when phase information is available.

I think we just need one number, the transaction timeout for wheel. If we aren't
latching for wheel, then we'll use 0ms, otherwise, we'll use the value of the
flag.

 
 class QueuedWebMouseWheelEvent;
 
@@ -47,7 +48,7 @@ class CONTENT_EXPORT MouseWheelEventQueue {
   // |scroll_transaction_ms| is the duration in which the
   // ScrollEnd should be sent after a ScrollUpdate.
   MouseWheelEventQueue(MouseWheelEventQueueClient* client,
-                       int64_t scroll_transaction_ms);
+                       bool touchpad_scroll_latching);
 
   ~MouseWheelEventQueue();
 
@@ -97,6 +98,9 @@ class CONTENT_EXPORT MouseWheelEventQueue {
   // GSB has been sent in the past.
   bool needs_scroll_end_;
 
+  // True if the touchpad scroll latching is enabled.
+  bool touchpad_scroll_latching_;
+
   int64_t scroll_transaction_ms_;
   blink::WebGestureDevice scrolling_device_;