Recipes: make cwd default to slave_build

scripts/slave/recipes/webrtc/chromium.expected/chromium_webrtc_fyi_Mac_GN__dbg_.json

Index: scripts/slave/recipes/webrtc/chromium.expected/chromium_webrtc_fyi_Mac_GN__dbg_.json
diff --git a/scripts/slave/recipes/webrtc/chromium.expected/chromium_webrtc_fyi_Mac_GN__dbg_.json b/scripts/slave/recipes/webrtc/chromium.expected/chromium_webrtc_fyi_Mac_GN__dbg_.json
index 62cf2ad74f4cf3c4b2583668b5fcb22e5c2b419f..614de638f65b7ea79c60f18292f82ecf2e74f04a 100644
--- a/scripts/slave/recipes/webrtc/chromium.expected/chromium_webrtc_fyi_Mac_GN__dbg_.json
+++ b/scripts/slave/recipes/webrtc/chromium.expected/chromium_webrtc_fyi_Mac_GN__dbg_.json
@@ -25,6 +25,7 @@
       "--revision",
       "src/third_party/webrtc@HEAD"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "bot_update",
     "~followup_annotations": [
       "@@@STEP_TEXT@Some step text@@@",
@@ -79,6 +80,7 @@
       "RECIPE_MODULE[webrtc]/resources/cleanup_files.py",
       "[SLAVE_BUILD]/src/out"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "clean test output files"
   },
   {
@@ -87,6 +89,7 @@
       "-u",
       "[BUILD]/scripts/slave/cleanup_temp.py"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "cleanup_temp"
   },
   {
@@ -96,6 +99,7 @@
       "[DEPOT_TOOLS]/gclient.py",
       "runhooks"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "env": {
       "GYP_CHROMIUM_NO_ACTION": "1"
     },
@@ -111,6 +115,7 @@
       "//out/Debug",
       "--args=is_debug=true target_cpu=\"x64\" use_goma=true goma_dir=\"[BUILD]/goma\""
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "gn"
   },
   {
@@ -131,6 +136,7 @@
       "--",
       "all"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "compile"
   }
 ]