Recipes: make cwd default to slave_build

scripts/slave/recipes/webrtc/standalone.expected/client_webrtc_mac64_debug__gn_.json

Index: scripts/slave/recipes/webrtc/standalone.expected/client_webrtc_mac64_debug__gn_.json
diff --git a/scripts/slave/recipes/webrtc/standalone.expected/client_webrtc_mac64_debug__gn_.json b/scripts/slave/recipes/webrtc/standalone.expected/client_webrtc_mac64_debug__gn_.json
index b0f125f528f2bd36300430855a57b32efa00f7f8..b4e47e9bd90f5d84da8159c2f1cdbcd77081f878 100644
--- a/scripts/slave/recipes/webrtc/standalone.expected/client_webrtc_mac64_debug__gn_.json
+++ b/scripts/slave/recipes/webrtc/standalone.expected/client_webrtc_mac64_debug__gn_.json
@@ -21,6 +21,7 @@
       "--revision",
       "src@12345"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "bot_update",
     "~followup_annotations": [
       "@@@STEP_TEXT@Some step text@@@",
@@ -47,6 +48,7 @@
       "RECIPE_MODULE[webrtc]/resources/cleanup_files.py",
       "[SLAVE_BUILD]/src/out"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "clean test output files"
   },
   {
@@ -55,6 +57,7 @@
       "-u",
       "[BUILD]/scripts/slave/cleanup_temp.py"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "cleanup_temp"
   },
   {
@@ -64,6 +67,7 @@
       "[DEPOT_TOOLS]/gclient.py",
       "runhooks"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "env": {
       "GYP_CHROMIUM_NO_ACTION": "1"
     },
@@ -79,6 +83,7 @@
       "//out/Debug",
       "--args=is_debug=true target_cpu=\"x64\" use_goma=true goma_dir=\"[BUILD]/goma\" build_with_chromium=false"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "gn"
   },
   {
@@ -99,6 +104,7 @@
       "--",
       "all"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "compile"
   }
 ]