Change the host_debug sky_shell used for testing to build with assertions enabled

scripts/slave/recipes/flutter/engine.expected/linux.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "\nimport os, sys\nfrom common import chromium_utils # Error? See https://crbug.com/584783.\n\npath = sys.argv[1]\nif os.path.exists(path):\n  for p in (os.path.join(path, x) for x in os.listdir(path)):\n    if os.path.isdir(p):\n      chromium_utils.RemoveDirectory(p)\n    else:\n      os.unlink(p)\n",
       "[SLAVE_BUILD]"
     ],
     "name": "rmcontents everything",
     "~followup_annotations": [
@@ skipping 118 matching lines @@
     "cmd": [
       "[SLAVE_BUILD]/src/tools/android/download_android_tools.py"
     ],
     "env": {
       "PATH": "[SLAVE_BUILD]/src/third_party/dart-sdk/dart-sdk/bin:%(PATH)s"
     },
     "name": "download android tools"
   },
   {
     "cmd": [
-      "[SLAVE_BUILD]/src/flutter/tools/gn"
+      "[SLAVE_BUILD]/src/flutter/tools/gn",
+      "--unoptimized"
     ],
     "env": {
       "PATH": "[SLAVE_BUILD]/src/third_party/dart-sdk/dart-sdk/bin:%(PATH)s"
     },
-    "name": "gn "
+    "name": "gn --unoptimized (2)"

[eseidel, 2016/08/19 19:44:40]

When names are not unique they get (2) appended, etc.  This can be worked around
by explicitly naming the step when calling api.step, which RunGN does under the
covers I'm sure.

   },
   {
     "cmd": [
       "ninja",
       "-C",
-      "[SLAVE_BUILD]/src/out/host_debug"
+      "[SLAVE_BUILD]/src/out/host_debug_unopt"
     ],
     "env": {
       "PATH": "[SLAVE_BUILD]/src/third_party/dart-sdk/dart-sdk/bin:%(PATH)s"
     },
-    "name": "build host_debug"
+    "name": "build host_debug_unopt"
   },
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_MODULE[build::zip]/resources/zip.py"
     ],
     "env": {
       "PATH": "[SLAVE_BUILD]/src/third_party/dart-sdk/dart-sdk/bin:%(PATH)s"
     },
     "name": "Zip linux-x64 artifacts.zip",
-    "stdin": "{\"entries\": [{\"archive_name\": \"icudtl.dat\", \"path\": \"[SLAVE_BUILD]/src/out/host_debug/icudtl.dat\", \"type\": \"file\"}, {\"archive_name\": \"sky_shell\", \"path\": \"[SLAVE_BUILD]/src/out/host_debug/sky_shell\", \"type\": \"file\"}, {\"archive_name\": \"sky_snapshot\", \"path\": \"[SLAVE_BUILD]/src/out/host_debug/sky_snapshot\", \"type\": \"file\"}], \"output\": \"[TMP_BASE]/tmp_tmp_1/artifacts.zip\", \"root\": \"[SLAVE_BUILD]/src\"}"
+    "stdin": "{\"entries\": [{\"archive_name\": \"icudtl.dat\", \"path\": \"[SLAVE_BUILD]/src/out/host_debug_unopt/icudtl.dat\", \"type\": \"file\"}, {\"archive_name\": \"sky_shell\", \"path\": \"[SLAVE_BUILD]/src/out/host_debug_unopt/sky_shell\", \"type\": \"file\"}, {\"archive_name\": \"sky_snapshot\", \"path\": \"[SLAVE_BUILD]/src/out/host_debug_unopt/sky_snapshot\", \"type\": \"file\"}], \"output\": \"[TMP_BASE]/tmp_tmp_1/artifacts.zip\", \"root\": \"[SLAVE_BUILD]/src\"}"
   },
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_MODULE[build::gsutil]/resources/gsutil_wrapper.py",
       "--",
       "RECIPE_PACKAGE_REPO[depot_tools]/gsutil.py",
       "----",
       "cp",
@@ skipping 27 matching lines @@
       "@@@STEP_LOG_LINE@python.inline@@@@",
       "@@@STEP_LOG_LINE@python.inline@if os.path.exists(sys.argv[1]):@@@",
       "@@@STEP_LOG_LINE@python.inline@  chromium_utils.RemoveDirectory(sys.argv[1])@@@",
       "@@@STEP_LOG_END@python.inline@@@"
     ]
   },
   {
     "cmd": [
       "dart",
       "[SLAVE_BUILD]/src/flutter/sky/shell/testing/observatory/test.dart",
-      "[SLAVE_BUILD]/src/out/host_debug/sky_shell",
+      "[SLAVE_BUILD]/src/out/host_debug_unopt/sky_shell",
       "[SLAVE_BUILD]/src/flutter/sky/shell/testing/observatory/empty_main.dart"
     ],
     "cwd": "[SLAVE_BUILD]/src",
     "env": {
       "PATH": "[SLAVE_BUILD]/src/third_party/dart-sdk/dart-sdk/bin:%(PATH)s"
     },
     "name": "test observatory and service protocol"
   },
   {
     "cmd": [
@@ skipping 871 matching lines @@
       "@@@STEP_LOG_LINE@python.inline@  chromium_utils.RemoveDirectory(sys.argv[1])@@@",
       "@@@STEP_LOG_END@python.inline@@@"
     ]
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]