BootManager: partition list scrolling with a BViewPort.

Fixes #7360.

src/apps/bootmanager/Jamfile

@@ -1,6 +1,7 @@
 SubDir HAIKU_TOP src apps bootmanager ;
 
 UsePrivateHeaders shared storage tracker ;
+UsePrivateHeaders interface ;
 
 local cataloguedSources =
 	BootDrive.cpp

src/apps/bootmanager/PartitionsPage.cpp

@@ -24,6 +24,7 @@
 #include <StringView.h>
 #include <TextControl.h>
 #include <TextView.h>
+#include <ViewPort.h>
 
 #include <StringForSize.h>
 
@@ -100,7 +101,9 @@ PartitionsPage::_BuildUI()
 		.SetColumnWeight(3, 0.5);
 	_FillPartitionsView(fPartitions);
 
-	BScrollView* scrollView = new BScrollView("scrollView", fPartitions, 0,
+	BViewPort* viewPort = new BViewPort(fPartitions);
+
+	BScrollView* scrollView = new BScrollView("scrollView", viewPort, 0,
 		false, true);
 
 	SetLayout(new BGroupLayout(B_VERTICAL));