Hello Abhishek,
Keep in mind that MSHTML implementation project is a very difficult one and most likely won't fit into GSoC timeframe. I would recommend you to choose from the other two if you are unsure about your skills. You would need to make an interface from MSHTML one to WebKit. MSHTML reference: https://msdn.microsoft.com/en-us/library/mt725313(v=vs.85).aspx
The Search project is about implementing the search band similar to Windows XP, search engine and support for Windows Search API. https://msdn.microsoft.com/en-us/library/windows/desktop/bb331575(v=vs.85).aspx
Sadly I can't comment on Recycle Bin project.
I hope this information helps in your search :)
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Cheers, Oleksandr.
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