[mac] Mark keys with cmd pressed as isSystemKeys.

webkit/api/src/mac/WebInputEventFactory.mm

Index: webkit/api/src/mac/WebInputEventFactory.mm
diff --git a/webkit/api/src/mac/WebInputEventFactory.mm b/webkit/api/src/mac/WebInputEventFactory.mm
index 74a7a8713a9c89b4a654b2539cc020ecea375260..5f29c50f7c5627f9c789527e4d18d38f0296da1f 100644
--- a/webkit/api/src/mac/WebInputEventFactory.mm
+++ b/webkit/api/src/mac/WebInputEventFactory.mm
@@ -919,6 +919,14 @@ WebKeyboardEvent WebInputEventFactory::keyboardEvent(NSEvent* event)
 
     result.timeStampSeconds = [event timestamp];
 
+    // Windows and Linux set that if alt is down. WebKit looks at this to decide
+    // if it should handle a key or not. E.g. alt-left/right shouldn't be used
+    // by webkit to scroll the current page, because we want to get that key
+    // back for it to do history navigation. Hence, the corresponding situation
+    // on OS X is to set this for cmd key presses.
+    if (result.modifiers & WebInputEvent::MetaKey)
+        result.isSystemKey = true;
+
     return result;
 }
 
@@ -938,6 +946,15 @@ WebKeyboardEvent WebInputEventFactory::keyboardEvent(wchar_t character,
     result.nativeKeyCode = character;
     result.text[0] = character;
     result.unmodifiedText[0] = character;
+
+    // Windows and Linux set that if alt is down. WebKit looks at this to decide
+    // if it should handle a key or not. E.g. alt-left/right shouldn't be used
+    // by webkit to scroll the current page, because we want to get that key
+    // back for it to do history navigation. Hence, the corresponding situation
+    // on OS X is to set this for cmd key presses.
+    if (result.modifiers & WebInputEvent::MetaKey)
+        result.isSystemKey = true;
+
     return result;
 }