Add suppresion of slop region touches in browser

content/browser/renderer_host/input/passthrough_touch_event_queue.cc

Index: content/browser/renderer_host/input/passthrough_touch_event_queue.cc
diff --git a/content/browser/renderer_host/input/passthrough_touch_event_queue.cc b/content/browser/renderer_host/input/passthrough_touch_event_queue.cc
index ae2131f38b84cd2b8d4aa9db36a4c9421ef34178..b9cc039df19a5282ef8f436436ea6276e7c92afd 100644
--- a/content/browser/renderer_host/input/passthrough_touch_event_queue.cc
+++ b/content/browser/renderer_host/input/passthrough_touch_event_queue.cc
@@ -24,6 +24,10 @@ using ui::LatencyInfo;
 namespace content {
 namespace {
 
+// A sanity check on touches received to ensure that touch movement outside
+// the platform slop region will cause scrolling.
+const double kMaxConceivablePlatformSlopRegionLengthDipsSquared = 60. * 60.;
+
 // Compare all properties of touch points to determine the state.
 bool HasPointChanged(const WebTouchPoint& point_1,
                      const WebTouchPoint& point_2) {
@@ -42,6 +46,59 @@ bool HasPointChanged(const WebTouchPoint& point_1,
 
 }  // namespace
 
+// Provides touchmove slop suppression for a touch sequence until a
+// (unprevented) touch will trigger immediate scrolling.
+class TouchMoveSlopSuppressor {
+ public:
+  TouchMoveSlopSuppressor() : suppressing_touchmoves_(false) {}
+
+  bool FilterEvent(const WebTouchEvent& event) {
+    if (WebTouchEventTraits::IsTouchSequenceStart(event)) {
+      suppressing_touchmoves_ = true;
+      touch_start_location_ = gfx::PointF(event.touches[0].position);
+    }
+
+    if (event.GetType() == WebInputEvent::kTouchEnd ||
+        event.GetType() == WebInputEvent::kTouchCancel)
+      suppressing_touchmoves_ = false;
+
+    if (event.GetType() != WebInputEvent::kTouchMove)
+      return false;
+
+    if (suppressing_touchmoves_) {
+      if (event.touches_length > 1) {
+        suppressing_touchmoves_ = false;
+      } else if (event.moved_beyond_slop_region) {
+        suppressing_touchmoves_ = false;
+      } else {
+        // No sane slop region should be larger than 60 DIPs.
+        DCHECK_LT(
+            (gfx::PointF(event.touches[0].position) - touch_start_location_)
+                .LengthSquared(),
+            kMaxConceivablePlatformSlopRegionLengthDipsSquared);
+      }
+    }
+
+    return suppressing_touchmoves_;
+  }
+
+  void ConfirmTouchEvent(InputEventAckState ack_result) {
+    if (ack_result == INPUT_EVENT_ACK_STATE_CONSUMED)
+      suppressing_touchmoves_ = false;
+  }
+
+  bool suppressing_touchmoves() const { return suppressing_touchmoves_; }
+
+ private:
+  bool suppressing_touchmoves_;
+
+  // Sanity check that the upstream touch provider is properly reporting whether
+  // the touch sequence will cause scrolling.
+  gfx::PointF touch_start_location_;
+
+  DISALLOW_COPY_AND_ASSIGN(TouchMoveSlopSuppressor);
+};
+
 PassthroughTouchEventQueue::TouchEventWithLatencyInfoAndAckState::
     TouchEventWithLatencyInfoAndAckState(const TouchEventWithLatencyInfo& event)
     : TouchEventWithLatencyInfo(event),
@@ -59,6 +116,7 @@ PassthroughTouchEventQueue::PassthroughTouchEventQueue(
       has_handlers_(true),
       maybe_has_handler_for_current_sequence_(false),
       drop_remaining_touches_in_sequence_(false),
+      touchmove_slop_suppressor_(new TouchMoveSlopSuppressor),
       send_touch_events_async_(false),
       processing_acks_(false) {
   if (config.touch_ack_timeout_supported) {
@@ -121,6 +179,8 @@ void PassthroughTouchEventQueue::ProcessTouchAck(
       timeout_handler_->ConfirmTouchEvent(unique_touch_event_id, ack_result))
     return;
 
+  touchmove_slop_suppressor_->ConfirmTouchEvent(ack_result);
+
   auto touch_event_iter = outstanding_touches_.begin();
   while (touch_event_iter != outstanding_touches_.end()) {
     if (unique_touch_event_id == touch_event_iter->event.unique_touch_event_id)
@@ -303,6 +363,9 @@ PassthroughTouchEventQueue::FilterBeforeForwarding(const WebTouchEvent& event) {
   if (timeout_handler_ && timeout_handler_->FilterEvent(event))
     return ACK_WITH_NO_CONSUMER_EXISTS;
 
+  if (touchmove_slop_suppressor_->FilterEvent(event))
+    return ACK_WITH_NOT_CONSUMED;
+
   if (drop_remaining_touches_in_sequence_ &&
       event.GetType() != WebInputEvent::kTouchCancel) {
     return ACK_WITH_NO_CONSUMER_EXISTS;