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The current behavior is that the select folder picker displays in desktop mode even when
when performed in ASH.

Fixes are as below:-
1. In the Chrome browser added plumbing in the SelectFileDialogImpl class to forward this
   operation of to the metro viewer process via the newly added function HandedSelectFolder
   which lives in the aura namespace in the remote_window_host_win.cc file.

2. In the metro viewer code added a new class FolderPickerSession which provides the functionality
   for displaying the metro select folder picker and returning the results from the same.

3. The following IPC messages provide the necessary functionality to funnel the request
   and the result between the browser and the metro viewer process.
   MetroViewerHostMsg_DisplaySelectFolder
   MetroViewerHostMsg_SelectFolderDone

I also added code to save away the metro root window in the RemoteRootWindowHostWin class
when we receive the MetroViewerHostMsg_SetTargetSurface IPC from the viewer process. We 
return this window in the RemoteRootWindowHostWin::GetAcceleratedWidget function. This
change although not needed for this CL seems correct. 

BUG=230087
R=cpu,sky

Review URL: https://codereview.chromium.org/14282002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@195224 0039d316-1c4b-4281-b951-d872f2087c98