[openjfx11][RFR] 8208114: Drag and drop of text contents and URL links functionalities are broken in Webview

[Arunprasad Rajkumar]

Hi,

Please review the following fix,

JBS: https://bugs.openjdk.java.net/browse/JDK-8208114

Root cause: 
It is a regression of JDK-8199474. DataTransfer mode should be set to readonly 
before calling DataTransfer::types, otherwise it will return empty mime type 
list while doing DnD. 

Solution: 
Move the temporary mode changing code before DataTransfer::types call. 

Webrev: 
http://cr.openjdk.java.net/~arajkumar/8208114/webrev 

Thanks,
Arun