Add support for Mac vs. Linux sky_server builds

DEPS

Index: DEPS
diff --git a/DEPS b/DEPS
index 9f5ba680a6b701604a485fb66e3398e72c779b58..5133110e2801047edc19728f02df5a9756342da6 100644
--- a/DEPS
+++ b/DEPS
@@ -251,6 +251,29 @@ hooks = [
                 '-s', 'src/buildtools/mac/clang-format.sha1',
     ],
   },
+  # Pull sky_server binaries using checked-in hashes.
+  {
+    'name': 'sky_server_linux',
+    'pattern': '.',
+    'action': [ 'download_from_google_storage',
+                '--no_resume',
+                '--platform=linux*',
+                '--no_auth',
+                '--bucket', 'mojo',
+                '-s', 'src/sky/tools/skygo/linux64/sky_server.sha1',
+    ],
+  },
+  {
+    'name': 'sky_server_mac',
+    'pattern': '.',
+    'action': [ 'download_from_google_storage',
+                '--no_resume',
+                '--platform=darwin',
+                '--no_auth',
+                '--bucket', 'mojo',
+                '-s', 'src/sky/tools/skygo/mac/sky_server.sha1',
+    ],
+  },
   # 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