Fix Chrome build for RecreateSKPs and CommandBuffer bots for GYP->GN

infra/bots/recipes/swarm_RecreateSKPs.expected/Housekeeper-Nightly-RecreateSKPs_Canary.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 66 matching lines @@
   },
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_PACKAGE_REPO[depot_tools]/gclient.py",
       "runhooks"
     ],
     "cwd": "[CUSTOM_/_B_WORK]",
     "env": {
+      "CPPFLAGS": "-DSK_ALLOW_CROSSPROCESS_PICTUREIMAGEFILTERS=1",
       "PATH": "%(PATH)s:RECIPE_PACKAGE_REPO[depot_tools]"
     },
     "name": "gclient runhooks"
   },
   {
     "cmd": [
       "python",
       "-u",
       "[CUSTOM_/_B_WORK]/skia/tools/buildbot_spec.py",
       "/path/to/tmp/json",
@@ skipping 47 matching lines @@
       "@@@STEP_LOG_LINE@python.inline@if not os.path.isdir(path):@@@",
       "@@@STEP_LOG_LINE@python.inline@  if os.path.exists(path):@@@",
       "@@@STEP_LOG_LINE@python.inline@    print \"%s exists but is not a dir\" % path@@@",
       "@@@STEP_LOG_LINE@python.inline@    sys.exit(1)@@@",
       "@@@STEP_LOG_LINE@python.inline@  os.makedirs(path, mode)@@@",
       "@@@STEP_LOG_END@python.inline@@@"
     ]
   },
   {
     "cmd": [
-      "python",
-      "-u",
-      "RECIPE_PACKAGE_REPO[depot_tools]/gclient.py",
-      "runhooks"
-    ],
-    "cwd": "[CUSTOM_/_B_WORK]/skia",
-    "env": {
-      "CPPFLAGS": "-DSK_ALLOW_CROSSPROCESS_PICTUREIMAGEFILTERS=1",
-      "PATH": "%(PATH)s:RECIPE_PACKAGE_REPO[depot_tools]"
-    },
-    "name": "gclient runhooks (2)"
-  },
-  {
-    "cmd": [
-      "build/gyp_chromium"
+      "[CUSTOM_/_B_WORK]/src/buildtools/linux64/gn",
+      "gen",
+      "[CUSTOM_/_B_WORK]/src/out/Release"
     ],
     "cwd": "[CUSTOM_/_B_WORK]/src",
     "env": {
       "CPPFLAGS": "-DSK_ALLOW_CROSSPROCESS_PICTUREIMAGEFILTERS=1",
       "GYP_GENERATORS": "ninja"
     },
-    "name": "gyp_chromium"
+    "name": "GN"
   },
   {
     "cmd": [
       "ninja",
       "-C",
-      "out/Release",
+      "[CUSTOM_/_B_WORK]/src/out/Release",
       "chrome"
     ],
     "cwd": "[CUSTOM_/_B_WORK]/src",
     "name": "Build Chrome"
   },
   {
     "cmd": [
       "python",
       "-u",
       "\nimport os\nimport urllib2\n\nBOTO_URL = 'http://metadata/computeMetadata/v1/project/attributes/boto-file'\n\ndest_path = '[SLAVE_BUILD]/tmp/.boto'\ndest_dir = os.path.dirname(dest_path)\nif not os.path.exists(dest_dir):\n  os.makedirs(dest_dir)\n\nreq = urllib2.Request(BOTO_URL, headers={'Metadata-Flavor': 'Google'})\ncontents = urllib2.urlopen(req).read()\n\nwith open(dest_path, 'w') as f:\n  f.write(contents)\n"
@@ skipping 79 matching lines @@
       "PATH": "[DEPOT_TOOLS]:%(PATH)s"
     },
     "name": "Recreate SKPs"
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]