Mac: Enable two finger double-tap smart zoom

Source/web/WebInputEventFactoryMac.mm

 /*
  * Copyright (C) 2004, 2006, 2007 Apple Inc. All rights reserved.
  * Copyright (C) 2006-2009 Google Inc.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 44 matching lines @@
 
 #endif  // __MAC_OS_X_VERSION_MAX_ALLOWED == 1060
 
 #if __MAC_OS_X_VERSION_MAX_ALLOWED < 1080
 
 // Additional Mountain Lion APIs.
 enum {
     NSEventPhaseMayBegin    = 0x1 << 5
 };
 
+enum {
+    NSEventTypeSmartMagnify = 32
+};
+
 #endif  // __MAC_OS_X_VERSION_MAX_ALLOWED < 1080
 
 namespace blink {
 
 static int windowsKeyCodeForKeyCode(uint16_t keyCode)
 {
     static const int windowsKeyCode[] = {
         /* 0 */ VK_A,
         /* 1 */ VK_S,
         /* 2 */ VK_D,
@@ skipping 1066 matching lines @@
 
     result.modifiers = modifiersFromEvent(event);
     result.timeStampSeconds = [event timestamp];
 
     result.sourceDevice = WebGestureDeviceTouchpad;
     switch ([event type]) {
     case NSEventTypeMagnify:
         result.type = WebInputEvent::GesturePinchUpdate;
         result.data.pinchUpdate.scale = [event magnification] + 1.0;
         break;
+    case NSEventTypeSmartMagnify:
+        result.type = WebInputEvent::GestureDoubleTap;

[aelias_OOO_until_Jul13, 2015/02/07 01:48:00]

I think this is worth a comment:

// Map the OS X "double-tap with two fingers" zoom gesture to regular
GestureDoubleTap, because the effect is similar to single-finger double-tap zoom
on mobile platforms.  Note that tapCount is intentionally 1 since the gesture
type already encodes the information.

[ccameron, 2015/02/07 08:19:41]

Good idea (and thanks for the wording suggestion).

+        result.data.tap.tapCount = 1;
+        break;
     case NSEventTypeBeginGesture:
     case NSEventTypeEndGesture:
         // The specific type of a gesture is not defined when the gesture begin
         // and end NSEvents come in. Leave them undefined. The caller will need
         // to specify them when the gesture is differentiated.
         result.type = WebInputEvent::Undefined;
         break;
     default:
         ASSERT_NOT_REACHED();
         result.type = WebInputEvent::Undefined;
     }
 
     return result;
 }
 
 } // namespace blink