Make .pyc cleaning optional in clean_local_files.

scripts/slave/recipes/webrtc/standalone.expected/client_webrtc_android32__m_nexus5x_.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "\nimport sys, os\npath = sys.argv[1]\nmode = int(sys.argv[2])\nif not os.path.isdir(path):\n  if os.path.exists(path):\n    print \"%s exists but is not a dir\" % path\n    sys.exit(1)\n  os.makedirs(path, mode)\n",
       "[BUILDER_CACHE]/Android32__M_Nexus5X_",
       "511"
     ],
     "name": "makedirs checkout path",
@@ skipping 67 matching lines @@
       "-u",
       "RECIPE_MODULE[build::webrtc]/resources/cleanup_files.py",
       "[BUILDER_CACHE]/Android32__M_Nexus5X_/src/out"
     ],
     "name": "clean test output files"
   },
   {
     "cmd": [
       "python",
       "-u",
-      "\nimport shutil, sys, os\nshutil.rmtree(sys.argv[1], True)\nshutil.rmtree(sys.argv[2], True)\ntry:\n  os.remove(sys.argv[3])\nexcept OSError:\n  pass\nfor base, _dirs, files in os.walk(sys.argv[4]):\n  for f in files:\n    if f.endswith('.pyc'):\n      os.remove(os.path.join(base, f))\n",
+      "\nimport shutil, sys, os\nshutil.rmtree(sys.argv[1], True)\nshutil.rmtree(sys.argv[2], True)\ntry:\n  os.remove(sys.argv[3])\nexcept OSError:\n  pass\n",
       "[BUILDER_CACHE]/Android32__M_Nexus5X_/src/out/Release/debug_info_dumps",
       "[BUILDER_CACHE]/Android32__M_Nexus5X_/src/out/Release/test_logs",
       "[BUILDER_CACHE]/Android32__M_Nexus5X_/src/out/build_product.zip",
       "[BUILDER_CACHE]/Android32__M_Nexus5X_/src"
     ],
     "name": "clean local files",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@python.inline@@@@",
       "@@@STEP_LOG_LINE@python.inline@import shutil, sys, os@@@",
       "@@@STEP_LOG_LINE@python.inline@shutil.rmtree(sys.argv[1], True)@@@",
       "@@@STEP_LOG_LINE@python.inline@shutil.rmtree(sys.argv[2], True)@@@",
       "@@@STEP_LOG_LINE@python.inline@try:@@@",
       "@@@STEP_LOG_LINE@python.inline@  os.remove(sys.argv[3])@@@",
       "@@@STEP_LOG_LINE@python.inline@except OSError:@@@",
       "@@@STEP_LOG_LINE@python.inline@  pass@@@",
-      "@@@STEP_LOG_LINE@python.inline@for base, _dirs, files in os.walk(sys.argv[4]):@@@",
-      "@@@STEP_LOG_LINE@python.inline@  for f in files:@@@",
-      "@@@STEP_LOG_LINE@python.inline@    if f.endswith('.pyc'):@@@",
-      "@@@STEP_LOG_LINE@python.inline@      os.remove(os.path.join(base, f))@@@",
       "@@@STEP_LOG_END@python.inline@@@"
     ]
   },
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_MODULE[build::isolate]/resources/find_isolated_tests.py",
       "--build-dir",
       "[BUILDER_CACHE]/Android32__M_Nexus5X_/src/out/Release",
@@ skipping 2545 matching lines @@
       "@@@STEP_LOG_END@json.output@@@",
       "@@@STEP_LINK@shard #0 isolated out@blah@@@"
     ]
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]