Align drag threshold across content types.

third_party/WebKit/Source/core/input/MouseEventManager.cpp

Index: third_party/WebKit/Source/core/input/MouseEventManager.cpp
diff --git a/third_party/WebKit/Source/core/input/MouseEventManager.cpp b/third_party/WebKit/Source/core/input/MouseEventManager.cpp
index 69e5522b9c03c87d9e4f5272453d16c18fc9c7e9..be8b40bf8330592b2b0cfb289ad1940997f2de65 100644
--- a/third_party/WebKit/Source/core/input/MouseEventManager.cpp
+++ b/third_party/WebKit/Source/core/input/MouseEventManager.cpp
@@ -59,20 +59,17 @@ PlatformMouseEvent mouseEventWithRegion(Node* node,
 // during a scroll.
 const double kFakeMouseMoveInterval = 0.1;
 
+// TODO(crbug.com/653490): Read these values from the OS.
 #if OS(MACOSX)
+const int kDragThresholdX = 3;
+const int kDragThresholdY = 3;
 const double kTextDragDelay = 0.15;
 #else
+const int kDragThresholdX = 4;
+const int kDragThresholdY = 4;
 const double kTextDragDelay = 0.0;
 #endif
 
-// The link drag hysteresis is much larger than the others because there
-// needs to be enough space to cancel the link press without starting a link
-// drag, and because dragging links is rare.
-const int kLinkDragHysteresis = 40;
-const int kImageDragHysteresis = 5;
-const int kTextDragHysteresis = 3;
-const int kGeneralDragHysteresis = 3;
-
 }  // namespace
 
 enum class DragInitiator { Mouse, Touch };
@@ -782,11 +779,11 @@ bool MouseEventManager::handleDrag(const MouseEventWithHitTestResults& event,
   m_frame->view()->setCursor(pointerCursor());
 
   if (initiator == DragInitiator::Mouse &&
-      !dragHysteresisExceeded(event.event().position()))
+      !dragThresholdExceeded(event.event().position()))
     return true;
 
-  // Once we're past the hysteresis point, we don't want to treat this gesture
-  // as a click
+  // Once we're past the drag threshold, we don't want to treat this gesture as
+  // a click.
   invalidateClick();
 
   if (!tryStartDrag(event)) {
@@ -930,7 +927,7 @@ DragState& MouseEventManager::dragState() {
   return state;
 }
 
-bool MouseEventManager::dragHysteresisExceeded(
+bool MouseEventManager::dragThresholdExceeded(
     const IntPoint& dragLocationInRootFrame) const {
   FrameView* view = m_frame->view();
   if (!view)
@@ -938,24 +935,14 @@ bool MouseEventManager::dragHysteresisExceeded(
   IntPoint dragLocation = view->rootFrameToContents(dragLocationInRootFrame);
   IntSize delta = dragLocation - m_mouseDownPos;
 
-  int threshold = kGeneralDragHysteresis;
-  switch (dragState().m_dragType) {
-    case DragSourceActionSelection:
-      threshold = kTextDragHysteresis;
-      break;
-    case DragSourceActionImage:
-      threshold = kImageDragHysteresis;
-      break;
-    case DragSourceActionLink:
-      threshold = kLinkDragHysteresis;
-      break;
-    case DragSourceActionDHTML:
-      break;
-    case DragSourceActionNone:
-      NOTREACHED();
-  }
+  int thresholdX = kDragThresholdX;
+  int thresholdY = kDragThresholdY;

[dcheng, 2016/10/20 09:11:55]

Nit: maybe just use the constants directly in the comparisons for now? When we
add the code to dynamically grab values from the system, then it'll make more
sense to have locals again.

[pwnall, 2016/10/20 09:47:46]

Done.

+
+  // WebKit's drag thresholds depend on the type of object being dragged. If we
+  // want to revive that behavior, we can multiply the thresholds above with a
+  // constant based on dragState().m_dragType.
 
-  return abs(delta.width()) >= threshold || abs(delta.height()) >= threshold;
+  return abs(delta.width()) >= thresholdX || abs(delta.height()) >= thresholdY;
 }
 
 void MouseEventManager::clearDragHeuristicState() {