Revert of Mac: Share kScrollbarPixelsPerCocoaTick between ui:: and blink:: events

ui/events/cocoa/events_mac.mm

Index: ui/events/cocoa/events_mac.mm
diff --git a/ui/events/cocoa/events_mac.mm b/ui/events/cocoa/events_mac.mm
index 48c955d7e17808db95bea6948dc4afe9d633bc02..dbfd64c7fdcd36360671423bdd98fca793366f23 100644
--- a/ui/events/cocoa/events_mac.mm
+++ b/ui/events/cocoa/events_mac.mm
@@ -140,7 +140,8 @@
 }
 
 gfx::Vector2d GetMouseWheelOffset(const base::NativeEvent& event) {
-  if ([event hasPreciseScrollingDeltas]) {
+  if ([event respondsToSelector:@selector(hasPreciseScrollingDeltas)] &&
+      [event hasPreciseScrollingDeltas]) {
     // Handle continuous scrolling devices such as a Magic Mouse or a trackpad.
     // -scrollingDelta{X|Y} have float return types but they return values that
     // are already rounded to integers.
@@ -152,11 +153,10 @@
     // values when scrolling up or to the left. Scrolling quickly results in a
     // higher delta per click, up to about 15.0. (Quartz documentation suggests
     // +/-10).
-    // Use the same multiplier as content::WebMouseWheelEventBuilder. Note this
-    // differs from the value returned by CGEventSourceGetPixelsPerLine(), which
-    // is typically 10.
-    return gfx::Vector2d(kScrollbarPixelsPerCocoaTick * [event deltaX],
-                         kScrollbarPixelsPerCocoaTick * [event deltaY]);
+    // Multiply by 1000 to vaguely approximate WHEEL_DELTA on Windows (120).
+    const CGFloat kWheelDeltaMultiplier = 1000;
+    return gfx::Vector2d(kWheelDeltaMultiplier * [event deltaX],
+                         kWheelDeltaMultiplier * [event deltaY]);
   }
 }