WebRTC: Add Libfuzzer commit and trybot.

scripts/slave/recipes/webrtc/libfuzzer.expected/full_tryserver_webrtc_linux_libfuzzer_rel.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "[BUILD]/scripts/slave/bot_update.py",
       "--master",
       "tryserver.webrtc",
       "--builder",
-      "linux_gn_rel",
+      "linux_libfuzzer_rel",
       "--slave",
-      "slavename",
+      "TestSlavename",
       "--spec",
       "cache_dir = None\nsolutions = [{'deps_file': 'DEPS', 'managed': True, 'name': 'src', 'url': 'https://chromium.googlesource.com/external/webrtc'}, {'deps_file': 'DEPS', 'managed': True, 'name': 'webrtc-limited', 'url': 'https://chrome-internal.googlesource.com/chrome/deps/webrtc-limited'}]",
       "--root",
       "src",
       "--revision_mapping_file",
       "{\"src\": \"got_revision\"}",
       "--issue",
-      "666666",
+      "12853011",
       "--patchset",
       "1",
       "--rietveld_server",
-      "https://fake.rietveld.url",
+      "https://codereview.chromium.org",
       "--output_json",
       "/path/to/tmp/json",
       "--revision",
-      "src@12345",
+      "src@HEAD",
       "--output_manifest"
     ],
     "cwd": "[SLAVE_BUILD]",
     "name": "bot_update",
     "~followup_annotations": [
       "@@@STEP_TEXT@Some step text@@@",
       "@@@STEP_LOG_LINE@json.output@{@@@",
       "@@@STEP_LOG_LINE@json.output@  \"did_run\": true, @@@",
       "@@@STEP_LOG_LINE@json.output@  \"manifest\": {@@@",
       "@@@STEP_LOG_LINE@json.output@    \"src\": {@@@",
@@ skipping 12 matching lines @@
       "@@@STEP_LOG_LINE@json.output@}@@@",
       "@@@STEP_LOG_END@json.output@@@",
       "@@@SET_BUILD_PROPERTY@got_revision@\"f27fede2220bcd326aee3e86ddfd4ebd0fe58cb9\"@@@",
       "@@@SET_BUILD_PROPERTY@got_revision_cp@\"refs/heads/master@{#170242}\"@@@"
     ]
   },
   {
     "cmd": [
       "python",
       "-u",
-      "RECIPE_MODULE[webrtc]/resources/cleanup_files.py",
-      "[SLAVE_BUILD]/src/out"
-    ],
-    "cwd": "[SLAVE_BUILD]",
-    "name": "clean test output files"
-  },
-  {
-    "cmd": [
-      "python",
-      "-u",
-      "[BUILD]/scripts/slave/cleanup_temp.py"
-    ],
-    "cwd": "[SLAVE_BUILD]",
-    "name": "cleanup_temp"
-  },
-  {
-    "cmd": [
-      "python",
-      "-u",
       "[DEPOT_TOOLS]/gclient.py",
       "runhooks"
     ],
     "cwd": "[SLAVE_BUILD]",
     "env": {
       "GYP_CHROMIUM_NO_ACTION": "1",
       "GYP_DEFINES": "component=static_library dcheck_always_on=1 fastbuild=1 gomadir='[BUILD]/goma' target_arch=x64 use_goma=1"
     },
     "name": "gclient runhooks"
   },
   {
     "cmd": [
+      "tools/clang/scripts/update.py",
+      "--force-local-build",
+      "--without-android"
+    ],
+    "cwd": "[SLAVE_BUILD]/src",
+    "env": {
+      "LLVM_FORCE_HEAD_REVISION": "YES"
+    },
+    "name": "checkout llvm"
+  },
+  {
+    "cmd": [
+      "python",
+      "-u",
+      "[DEPOT_TOOLS]/gn.py",
+      "--root=[SLAVE_BUILD]/src",
+      "gen",
+      "//out/Release",
+      "--args=use_libfuzzer=true is_asan=true is_debug=false target_cpu=\"x64\""
+    ],
+    "cwd": "[SLAVE_BUILD]",
+    "name": "gn"
+  },
+  {
+    "cmd": [
       "python",
       "-u",
       "[DEPOT_TOOLS]/gn.py",
       "--root=[SLAVE_BUILD]/src",
-      "gen",
-      "//out/Release",
-      "--args=is_debug=false target_cpu=\"x64\" use_goma=true goma_dir=\"[BUILD]/goma\""
+      "refs",
+      "[SLAVE_BUILD]/src/out/Release",
+      "--all",
+      "--type=executable",
+      "--args=\"use_libfuzzer=true is_asan=true\"",
+      "--as=output",
+      "//webrtc/test/fuzzers:webrtc_fuzzer_main"
     ],
     "cwd": "[SLAVE_BUILD]",
-    "name": "gn"
+    "name": "calculate targets",
+    "stdout": "/path/to/tmp/",
+    "~followup_annotations": [
+      "@@@STEP_LOG_LINE@targets@target1@@@",
+      "@@@STEP_LOG_LINE@targets@target2@@@",
+      "@@@STEP_LOG_LINE@targets@target3@@@",
+      "@@@STEP_LOG_END@targets@@@"
+    ]
   },
   {
     "cmd": [
       "python",
       "-u",
       "[BUILD]/scripts/slave/compile.py",
       "--target",
       "Release",
       "--src-dir",
       "[SLAVE_BUILD]/src",
       "--build-tool",
       "ninja",
       "--compiler",
       "goma",
       "--goma-jsonstatus",
       "/path/to/tmp/json",
       "--goma-dir",
       "[BUILD]/goma",
       "--goma-fail-fast",
       "--goma-disable-local-fallback",
       "--",
-      "all"
+      "target1",
+      "target2",
+      "target3"
     ],
     "cwd": "[SLAVE_BUILD]",
     "name": "compile",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@json.output (invalid)@null@@@",
       "@@@STEP_LOG_END@json.output (invalid)@@@"
     ]
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]