GN: Don't depend on dart_bootstrap if there is a usable prebuilt sdk

build/gn_run_binary.py

Index: build/gn_run_binary.py
diff --git a/build/gn_run_binary.py b/build/gn_run_binary.py
index 7d83f6136fd70e05e0c3628b527a094f1b69a2b8..4767bc6ee0c1e66651a9fb81e2b5bb562a4d4bb0 100644
--- a/build/gn_run_binary.py
+++ b/build/gn_run_binary.py
@@ -8,15 +8,28 @@ Run with:
   python gn_run_binary.py <binary_name> [args ...]
 """
 
+import os
 import sys
 import subprocess
 
-# This script is designed to run binaries produced by the current build. We
-# always prefix it with "./" to avoid picking up system versions that might
-# also be on the path.
-path = './' + sys.argv[1]
+# Run a command, swallowing the output unless there is an error.
+def run_command(command):
+  try:
+    subprocess.check_output(command, stderr=subprocess.STDOUT)
+    return 0
+  except subprocess.CalledProcessError as e:
+    return ("Command failed: " + ' '.join(command) + "\n" +
+            "output: " + e.output)
+
+# Unless the path is absolute, this script is designed to run binaries produced
+# by the current build. We always prefix it with "./" to avoid picking up system
+# versions that might also be on the path.
+if os.path.isabs(sys.argv[1]):
+  path = sys.argv[1]
+else:
+  path = './' + sys.argv[1]
 
 # The rest of the arguements are passed directly to the executable.
 args = [path] + sys.argv[2:]
 
-sys.exit(subprocess.call(args))
+sys.exit(run_command(args))