Recipes: make cwd default to slave_build

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

Index: scripts/slave/recipes/webrtc/chromium.expected/chromium_webrtc_fyi_Win_GN__dbg_.json
diff --git a/scripts/slave/recipes/webrtc/chromium.expected/chromium_webrtc_fyi_Win_GN__dbg_.json b/scripts/slave/recipes/webrtc/chromium.expected/chromium_webrtc_fyi_Win_GN__dbg_.json
index b1ace9009f2b9fc94a10e56c3ed598707e50893b..c8979261490f0c139f6739a642b2b106e8074921 100644
--- a/scripts/slave/recipes/webrtc/chromium.expected/chromium_webrtc_fyi_Win_GN__dbg_.json
+++ b/scripts/slave/recipes/webrtc/chromium.expected/chromium_webrtc_fyi_Win_GN__dbg_.json
@@ -5,6 +5,7 @@
       "-u",
       "[BUILD]\\scripts\\slave\\kill_processes.py"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "taskkill"
   },
   {
@@ -33,6 +34,7 @@
       "--revision",
       "src/third_party/webrtc@HEAD"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "bot_update",
     "~followup_annotations": [
       "@@@STEP_TEXT@Some step text@@@",
@@ -87,6 +89,7 @@
       "RECIPE_MODULE[webrtc]\\resources\\cleanup_files.py",
       "[SLAVE_BUILD]\\src\\out"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "clean test output files"
   },
   {
@@ -95,6 +98,7 @@
       "-u",
       "[BUILD]\\scripts\\slave\\cleanup_temp.py"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "cleanup_temp"
   },
   {
@@ -104,6 +108,7 @@
       "[DEPOT_TOOLS]\\gclient.py",
       "runhooks"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "env": {
       "GYP_CHROMIUM_NO_ACTION": "1"
     },
@@ -119,6 +124,7 @@
       "//out/Debug",
       "--args=symbol_level=1 is_debug=true target_cpu=\"x86\" host_cpu=\"x86\" use_goma=true goma_dir=\"[BUILD]\\goma\""
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "gn"
   },
   {
@@ -139,6 +145,7 @@
       "--",
       "all"
     ],
+    "cwd": "[SLAVE_BUILD]",
     "name": "compile"
   }
 ]