runtime: in runtime-gdb.py, use SliceValue wrapper

Rather than reaching in to slices directly in the slice pretty
printer, use the newly introduced SliceValue wrapper.

Change-Id: Ibb25f8c618c2ffb3fe1a8dd044bb9a6a085df5b7
Reviewed-on: https://go-review.googlesource.com/4936Reviewed-by: Minux Ma <minux@golang.org>

src/runtime/runtime-gdb.py

@@ -88,11 +88,11 @@ class SliceTypePrinter:
 		return str(self.val.type)[6:]  # skip 'struct '
 
 	def children(self):
-		if self.val["len"] > self.val["cap"]:
+		sval = SliceValue(self.val)
+		if sval.len > sval.cap:
 			return
-		ptr = self.val["array"]
-		for idx in range(int(self.val["len"])):
-			yield ('[{0}]'.format(idx), (ptr + idx).dereference())
+		for idx, item in enumerate(sval):
+			yield ('[{0}]'.format(idx), item)
 
 
 class MapTypePrinter: