partially revert f6f7181 to fix #165

content/app_shim_remote_cocoa/render_widget_host_view_cocoa.mm

@@ -13,6 +13,7 @@
 
 #include "base/containers/contains.h"
 #include "base/debug/crash_logging.h"
+#include "base/mac/mac_util.h"
 #import "base/mac/foundation_util.h"
 #include "base/strings/sys_string_conversions.h"
 #include "components/remote_cocoa/app_shim/ns_view_ids.h"
@@ -1404,6 +1405,27 @@ - (void)scrollWheel:(NSEvent*)event {
 
 // Called repeatedly during a pinch gesture, with incremental change values.
 - (void)magnifyWithEvent:(NSEvent*)event {
+  if (base::mac::IsAtLeastOS10_11()) {
+    if (event.phase == NSEventPhaseBegan) {
+      [self handleBeginGestureWithEvent:event isSyntheticallyInjected:NO];
+      return;
+    }
+
+    if (event.phase == NSEventPhaseEnded ||
+        event.phase == NSEventPhaseCancelled) {
+      [self handleEndGestureWithEvent:event];
+      return;
+    }
+  }
+
+  // If this conditional evalutes to true, and the function has not
+  // short-circuited from the previous block, then this event is a duplicate of
+  // a gesture event, and should be ignored.
+  if (event.phase == NSEventPhaseBegan || event.phase == NSEventPhaseEnded ||
+      event.phase == NSEventPhaseCancelled) {
+    return;
+  }
+
   WebGestureEvent updateEvent = WebGestureEventBuilder::Build(event, self);
   _hostHelper->GestureUpdate(updateEvent);
 }