[swarming] Add luci-go's isolate tool, downloaded via runhooks.

DEPS

 # Note: The buildbots evaluate this file with CWD set to the parent
 # directory and assume that the root of the checkout is in ./v8/, so
 # all paths in here must match this assumption.
 
 vars = {
   "git_url": "https://chromium.googlesource.com",
 }
 
 deps = {
   "v8/build/gyp":
@@ skipping 75 matching lines @@
     "name": "clang_format_linux",
     "pattern": ".",
     "action": [ "download_from_google_storage",
                 "--no_resume",
                 "--platform=linux*",
                 "--no_auth",
                 "--bucket", "chromium-clang-format",
                 "-s", "v8/buildtools/linux64/clang-format.sha1",
     ],
   },
+  # Pull luci-go binaries (isolate, swarming) using checked-in hashes.
+  {
+    'name': 'luci-go_win',
+    'pattern': '.',
+    'action': [ 'download_from_google_storage',
+                '--no_resume',
+                '--platform=win32',
+                '--no_auth',
+                '--bucket', 'chromium-luci',
+                '-d', 'v8/tools/luci-go/win64',
+    ],
+  },
+  {
+    'name': 'luci-go_mac',
+    'pattern': '.',
+    'action': [ 'download_from_google_storage',
+                '--no_resume',
+                '--platform=darwin',
+                '--no_auth',
+                '--bucket', 'chromium-luci',
+                '-d', 'v8/tools/luci-go/mac64',
+    ],
+  },
+  {
+    'name': 'luci-go_linux',
+    'pattern': '.',
+    'action': [ 'download_from_google_storage',
+                '--no_resume',
+                '--platform=linux*',
+                '--no_auth',
+                '--bucket', 'chromium-luci',
+                '-d', 'v8/tools/luci-go/linux64',
+    ],
+  },
   # Pull binutils for linux, enabled debug fission for faster linking /
   # debugging when used with clang on Ubuntu Precise.
   # https://code.google.com/p/chromium/issues/detail?id=352046
   {
     'name': 'binutils',
     'pattern': 'v8/third_party/binutils',
     'action': [
         'python',
         'v8/third_party/binutils/download.py',
     ],
@@ skipping 11 matching lines @@
     'name': 'clang',
     'pattern': '.',
     'action': ['python', 'v8/tools/clang/scripts/update.py', '--if-needed'],
   },
   {
     # A change to a .gyp, .gypi, or to GYP itself should run the generator.
     "pattern": ".",
     "action": ["python", "v8/build/gyp_v8"],
   },
 ]