bin/sync-and-gyp: better error checking

bin/sync-and-gyp

 #!/usr/bin/env python
 
 # Copyright 2015 Google Inc.
 #
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # This script will update Skia's dependencies as necessary and run
 # gyp if needed.
 
@@ skipping 58 matching lines @@
     "managed"     : False,
     "custom_deps" : {
     },
     "safesync_url": "",
   },
 ]
 cache_dir = None
 '''
 if current_deps_hash != deps_hash:
   # `gclient sync` is very slow, so skip whenever we can.
+  try:
+    subprocess.call(['gclient', '--version'])
+  except:
+    sys.stdout.write('gclient missing from $PATH, please install ' +
+                     'depot_tools\n    https://skia.org/user/quick/desktop\n')
+    exit(1)
   if not os.path.isfile('.gclient'):
     with open('.gclient', 'w') as o:
       o.write(default_gclient_config)
   gclient_sync_command = ['gclient', 'sync'] + skia_opt_deps
   try:
     sys.stdout.write('%r\n' % gclient_sync_command)
     subprocess.check_call(gclient_sync_command)
   except:
     sys.stderr.write('\n`gclient sync` failed.\n')
-    os.remove('.deps_sha1')  # Unknown state.
+    try:
+      os.remove('.deps_sha1')  # Unknown state.
+    except:
+      pass
     exit(1)
   # Only write hash after a successful sync.
   with open('.deps_sha1', 'w') as o:
     o.write(deps_hash)
 
 hasher = hashlib.sha1()
 
 for var in ['AR', 'AR_host', 'AR_target',
             'CC', 'CC_host', 'CC_target',
             'CFLAGS', 'CFLAGS_host',
@@ skipping 26 matching lines @@
       return f.read()
   return ''
 
 if cat_if_exists(hash_path).strip() != gyp_hash:
   env = os.environ.copy()
   if skia_out:
     env['SKIA_OUT'] = skia_out
   subprocess.call(['python', './gyp_skia'], env=env)
   with open(hash_path, 'w') as o:
     o.write(gyp_hash)