GN: take over CommandBuffer bot

infra/bots/recipes/swarm_compile.expected/Build-Mac-Clang-x86_64-Debug-CommandBuffer.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "\nimport sys, os\npath = sys.argv[1]\nmode = int(sys.argv[2])\nif not os.path.isdir(path):\n  if os.path.exists(path):\n    print \"%s exists but is not a dir\" % path\n    sys.exit(1)\n  os.makedirs(path, mode)\n",
       "[CUSTOM_/_B_WORK]",
       "511"
     ],
     "name": "makedirs checkout_path",
@@ skipping 122 matching lines @@
     ],
     "cwd": "[CUSTOM_/_B_WORK]",
     "env": {
       "GYP_CHROMIUM_NO_ACTION": "0",
       "PATH": "%(PATH)s:RECIPE_PACKAGE_REPO[depot_tools]"
     },
     "name": "gclient runhooks"
   },
   {
     "cmd": [
-      "make",
-      "most"
-    ],
-    "cwd": "[CUSTOM_/_B_WORK]/skia",
-    "env": {
-      "BUILDTYPE": "Debug",
-      "CC": "/usr/bin/clang",
-      "CHROME_HEADLESS": "1",
-      "CHROME_PATH": "[SLAVE_BUILD]/src",
-      "CXX": "/usr/bin/clang++",
-      "GYP_DEFINES": "skia_arch_type=x86_64 skia_clang_build=1 skia_command_buffer=1 skia_warnings_as_errors=1",
-      "PATH": "%(PATH)s:RECIPE_PACKAGE_REPO[depot_tools]:RECIPE_PACKAGE_REPO[depot_tools]:RECIPE_PACKAGE_REPO[depot_tools]:RECIPE_PACKAGE_REPO[depot_tools]",
-      "SKIA_OUT": "[CUSTOM_/_B_WORK]/skia/out/Build-Mac-Clang-x86_64-Debug-CommandBuffer"
-    },
-    "name": "build most"
-  },
-  {
-    "cmd": [
       "python",
       "-u",
       "[CUSTOM_/_B_WORK]/skia/tools/build_command_buffer.py",
       "--chrome-dir",
       "[CUSTOM_/_B_WORK]",
       "--output-dir",
       "[CUSTOM_/_B_WORK]/skia/out/Build-Mac-Clang-x86_64-Debug-CommandBuffer/Debug",
       "--chrome-build-type",
       "Debug",
-      "--no-sync"
+      "--no-sync",
+      "--make-output-dir"
     ],
     "env": {
       "BUILDTYPE": "Debug",
-      "CC": "/usr/bin/clang",
       "CHROME_HEADLESS": "1",
-      "CHROME_PATH": "[SLAVE_BUILD]/src",
-      "CXX": "/usr/bin/clang++",
-      "GYP_DEFINES": "skia_arch_type=x86_64 skia_clang_build=1 skia_command_buffer=1 skia_warnings_as_errors=1",
       "PATH": "%(PATH)s:RECIPE_PACKAGE_REPO[depot_tools]:RECIPE_PACKAGE_REPO[depot_tools]:RECIPE_PACKAGE_REPO[depot_tools]:RECIPE_PACKAGE_REPO[depot_tools]",
       "SKIA_OUT": "[CUSTOM_/_B_WORK]/skia/out/Build-Mac-Clang-x86_64-Debug-CommandBuffer"
     },
     "name": "build command_buffer"
   },
   {
     "cmd": [
+      "[CUSTOM_/_B_WORK]/skia/bin/fetch-gn"
+    ],
+    "cwd": "[CUSTOM_/_B_WORK]/skia",
+    "env": {
+      "PATH": "%(PATH)s:RECIPE_PACKAGE_REPO[depot_tools]:RECIPE_PACKAGE_REPO[depot_tools]:RECIPE_PACKAGE_REPO[depot_tools]:RECIPE_PACKAGE_REPO[depot_tools]"
+    },
+    "name": "fetch-gn"
+  },
+  {
+    "cmd": [
+      "gn",
+      "gen",
+      "[CUSTOM_/_B_WORK]/skia/out/Build-Mac-Clang-x86_64-Debug-CommandBuffer/Debug",
+      "--args=cc=\"clang\" cxx=\"clang++\""
+    ],
+    "cwd": "[CUSTOM_/_B_WORK]/skia",
+    "env": {
+      "PATH": "%(PATH)s:RECIPE_PACKAGE_REPO[depot_tools]:RECIPE_PACKAGE_REPO[depot_tools]:RECIPE_PACKAGE_REPO[depot_tools]:RECIPE_PACKAGE_REPO[depot_tools]"
+    },
+    "name": "gn gen"
+  },
+  {
+    "cmd": [
+      "ninja",
+      "-C",
+      "[CUSTOM_/_B_WORK]/skia/out/Build-Mac-Clang-x86_64-Debug-CommandBuffer/Debug"
+    ],
+    "cwd": "[CUSTOM_/_B_WORK]/skia",
+    "env": {
+      "PATH": "%(PATH)s:RECIPE_PACKAGE_REPO[depot_tools]:RECIPE_PACKAGE_REPO[depot_tools]:RECIPE_PACKAGE_REPO[depot_tools]:RECIPE_PACKAGE_REPO[depot_tools]"
+    },
+    "name": "ninja"
+  },
+  {
+    "cmd": [
       "python",
       "-u",
       "import errno\nimport glob\nimport os\nimport shutil\nimport sys\n\nsrc = sys.argv[1]\ndst = sys.argv[2]\nbuild_products_whitelist = ['dm', 'dm.exe', 'get_images_from_skps', 'get_images_from_skps.exe', 'nanobench', 'nanobench.exe', '*.so', '*.dll', '*.dylib', 'skia_launcher', 'lib/*.so', 'iOSShell.app', 'iOSShell.ipa', 'visualbench', 'visualbench.exe', 'vulkan-1.dll']\n\ntry:\n  os.makedirs(dst)\nexcept OSError as e:\n  if e.errno != errno.EEXIST:\n    raise\n\nfor pattern in build_products_whitelist:\n  path = os.path.join(src, pattern)\n  for f in glob.glob(path):\n    dst_path = os.path.join(dst, os.path.relpath(f, src))\n    if not os.path.isdir(os.path.dirname(dst_path)):\n      os.makedirs(os.path.dirname(dst_path))\n    print 'Copying build product %s to %s' % (f, dst_path)\n    shutil.move(f, dst_path)\n",
       "[CUSTOM_/_B_WORK]/skia/out/Build-Mac-Clang-x86_64-Debug-CommandBuffer/Debug",
       "[CUSTOM_[SWARM_OUT_DIR]]/out/Debug"
     ],
     "name": "copy build products",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@python.inline@import errno@@@",
       "@@@STEP_LOG_LINE@python.inline@import glob@@@",
@@ skipping 21 matching lines @@
       "@@@STEP_LOG_LINE@python.inline@    shutil.move(f, dst_path)@@@",
       "@@@STEP_LOG_END@python.inline@@@"
     ]
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]