Should set the modifiers for web mouse event on Mac.

Source/web/WebInputEventFactoryMac.mm

Index: Source/web/WebInputEventFactoryMac.mm
diff --git a/Source/web/WebInputEventFactoryMac.mm b/Source/web/WebInputEventFactoryMac.mm
index e71b93ce071dfecab22ef8c652ff42fa0ca90142..fcdde0dbd1a81fe48c39c588ff00b30a6fdaa62b 100644
--- a/Source/web/WebInputEventFactoryMac.mm
+++ b/Source/web/WebInputEventFactoryMac.mm
@@ -722,7 +722,12 @@ static inline int modifiersFromEvent(NSEvent* event) {
         modifiers |= WebInputEvent::MetaKey;
     if ([event modifierFlags] & NSAlphaShiftKeyMask)
         modifiers |= WebInputEvent::CapsLockOn;
-    // TODO(port): Set mouse button states
+    if ([NSEvent pressedMouseButtons] & 1 << 0)

[haraken, 2014/12/11 16:24:13]

Don't we want to have a constant variable for 1 << 0? At least, let's add '('
and ')' around 1 << 0.

[zino, 2014/12/11 17:01:28]

Done.

IMHO, it is better to use constant values here than constant variables.
Because the values will be used only here.
I added some comments instead.

+        modifiers |= WebInputEvent::LeftButtonDown;
+    if ([NSEvent pressedMouseButtons] & 1 << 1)
+        modifiers |= WebInputEvent::RightButtonDown;
+    if ([NSEvent pressedMouseButtons] & 1 << 2)
+        modifiers |= WebInputEvent::MiddleButtonDown;
 
     return modifiers;
 }