Fix a flash plugin process crash on Windows which occurs on the field in the context of the SetCu...

Fix a flash plugin process crash on Windows which occurs on the field in the context of the SetCursor Windows API
call. We intercept this API to ensure that custom cursors set by flash plugin can be marshaled back to the browser
process. Based on the callstack the crash occurs while clearing the custom data vector in the WebCursor object
in the plugin process. As this field is not used on Windows, it is not clear why this crash occurs. It may well
be due to the fact that the global plugin instance pointer is pointing to an invalid plugin instance. Code inspection
did not reveal much.

We don't need to save away the plugin cursor in the SetCursor intercept. This can be safely done in the HandleEvent
handler, which simplifies the code and should hopefully fix this crash.

Fixes bug http://code.google.com/p/chromium/issues/detail?id=96282

BUG=96282
Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=102313

[jam, 2011-09-22 18:19:41]

lgtm