Revert of Remove enable/disable wheel gestures setting.

content/browser/renderer_host/render_widget_host_view_mac.mm

Index: content/browser/renderer_host/render_widget_host_view_mac.mm
diff --git a/content/browser/renderer_host/render_widget_host_view_mac.mm b/content/browser/renderer_host/render_widget_host_view_mac.mm
index ff0893069765ecd117ddb1f39efa90c31e76f1a8..11e91776c92484cc08ac959f2762ef7f20caf45b 100644
--- a/content/browser/renderer_host/render_widget_host_view_mac.mm
+++ b/content/browser/renderer_host/render_widget_host_view_mac.mm
@@ -52,6 +52,7 @@
 #import "content/browser/renderer_host/text_input_client_mac.h"
 #include "content/common/accessibility_messages.h"
 #include "content/common/edit_command.h"
+#include "content/common/input/input_event_utils.h"
 #include "content/common/input_messages.h"
 #include "content/common/site_isolation_policy.h"
 #include "content/common/text_input_state.h"
@@ -562,6 +563,7 @@
       is_loading_(false),
       allow_pause_for_resize_or_repaint_(true),
       is_guest_view_hack_(is_guest_view_hack),
+      wheel_gestures_enabled_(UseGestureBasedWheelScrolling()),
       fullscreen_parent_host_view_(nullptr),
       begin_frame_source_(nullptr),
       needs_begin_frames_(false),
@@ -1573,6 +1575,20 @@
 
   if (render_widget_host_)
     render_widget_host_->LostMouseLock();
+}
+
+void RenderWidgetHostViewMac::WheelEventAck(
+    const blink::WebMouseWheelEvent& event,
+    InputEventAckState ack_result) {
+  // TODO(dtapuska): Remove this handling of the wheel event ack
+  // once wheel gestures is enabled for a full release; see crbug.com/598798.
+  if (wheel_gestures_enabled_)
+    return;
+  bool consumed = ack_result == INPUT_EVENT_ACK_STATE_CONSUMED;
+  // Only record a wheel event as unhandled if JavaScript handlers got a chance
+  // to see it (no-op wheel events are ignored by the event dispatcher)
+  if (event.deltaX || event.deltaY)
+    [cocoa_view_ processedWheelEvent:event consumed:consumed];
 }
 
 void RenderWidgetHostViewMac::GestureEventAck(