Download the dart sdk into third_party/.

DEPS

 # This file is automatically processed to create .DEPS.git which is the file
 # that gclient uses under git.
 #
 # See http://code.google.com/p/chromium/wiki/UsingGit
 #
 # To test manually, run:
 #   python tools/deps2git/deps2git.py -o .DEPS.git -w <gclientdir>
 # where <gcliendir> is the absolute path to the directory containing the
 # .gclient file (the parent of 'src').
 #
@@ skipping 217 matching lines @@
     'action': ['python', 'src/build/linux/install-arm-sysroot.py',
                '--linux-only'],
   },
   {
     # Pull clang if needed or requested via GYP_DEFINES.
     'name': 'clang',
     'pattern': '.',
     'action': ['python', 'src/tools/clang/scripts/update.py', '--if-needed'],
   },
   {
+    # Pull dart sdk if needed
+    'name': 'dart',
+    'pattern': '.',
+    'action': ['python', 'src/tools/dart/update.py'],
+  },
+  {
     # Update the Windows toolchain if necessary.
     'name': 'win_toolchain',
     'pattern': '.',
     'action': ['python', 'src/build/vs_toolchain.py', 'update'],
   },
   {
     # Update LASTCHANGE. This is also run by export_tarball.py in
     # src/tools/export_tarball - please keep them in sync.
     'name': 'lastchange',
     'pattern': '.',
@@ skipping 84 matching lines @@
     # corresponding .py files have already been deleted.
     'name': 'remove_stale_pyc_files',
     'pattern': 'src/tools/.*\\.py',
     'action': [
         'python',
         'src/tools/remove_stale_pyc_files.py',
         'src/tools',
     ],
   },
 ]