statprof: use context manager for file when writing flame graph

Differential Revision: https://phab.mercurial-scm.org/D6780

mercurial/statprof.py

@@ -729,10 +729,6 b' def write_to_flame(data, fp, scriptpath='
         fp.write(b'get it here: https://github.com/brendangregg/FlameGraph\n')
         return
 
-    fd, path = pycompat.mkstemp()
-
-    file = open(path, "w+")
-
     lines = {}
     for sample in data.samples:
         sites = [s.function for s in sample.stack]
@@ -743,11 +739,12 b' def write_to_flame(data, fp, scriptpath='
         else:
             lines[line] = 1
 
+    fd, path = pycompat.mkstemp()
+
+    with open(path, "w+") as file:
     for line, count in lines.iteritems():
         file.write("%s %d\n" % (line, count))
 
-    file.close()
-
     if outputfile is None:
         outputfile = '~/flamegraph.svg'