Breakdown memory usage by source file names in dmprof.

tools/deep_memory_profiler/policies.json

 {
+  "sourcefile": {
+    "file": "policy.sourcefile.json",
+    "format": "json"
+  },
   "l0": {
     "file": "policy.l0.json",
     "format": "json"
   },
   "l1": {
     "file": "policy.l1.json",
     "format": "json"
   },
   "l2": {
     "file": "policy.l2.json",
     "format": "json"
   },
   "t0": {
     "file": "policy.t0.json",
     "format": "json"
   }
 }