Recipes: make cwd default to slave_build

scripts/slave/recipes/webrtc/standalone.expected/tryserver_webrtc_mac_x64_gn_rel.json

Index: scripts/slave/recipes/webrtc/standalone.expected/tryserver_webrtc_mac_x64_gn_rel.json
diff --git a/scripts/slave/recipes/webrtc/standalone.expected/tryserver_webrtc_mac_x64_gn_rel.json b/scripts/slave/recipes/webrtc/standalone.expected/tryserver_webrtc_mac_x64_gn_rel.json
index 356d95ef6726c7caa86a42a7bfb1aece300d8d0b..f300597fb593eb9bec9a2da923e52228b6f20685 100644
--- a/scripts/slave/recipes/webrtc/standalone.expected/tryserver_webrtc_mac_x64_gn_rel.json
+++ b/scripts/slave/recipes/webrtc/standalone.expected/tryserver_webrtc_mac_x64_gn_rel.json
@@ -27,6 +27,7 @@
       "--revision",
       "src@12345"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "bot_update",
     "~followup_annotations": [
       "@@@STEP_TEXT@Some step text@@@",
@@ -53,6 +54,7 @@
       "RECIPE_MODULE[webrtc]/resources/cleanup_files.py",
       "[SLAVE_BUILD]/src/out"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "clean test output files"
   },
   {
@@ -61,6 +63,7 @@
       "-u",
       "[BUILD]/scripts/slave/cleanup_temp.py"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "cleanup_temp"
   },
   {
@@ -70,6 +73,7 @@
       "[DEPOT_TOOLS]/gclient.py",
       "runhooks"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "env": {
       "GYP_CHROMIUM_NO_ACTION": "1"
     },
@@ -85,6 +89,7 @@
       "//out/Release",
       "--args=is_debug=false target_cpu=\"x64\" use_goma=true goma_dir=\"[BUILD]/goma\" build_with_chromium=false"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "gn"
   },
   {
@@ -105,6 +110,7 @@
       "--",
       "all"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "compile"
   }
 ]