Upload/Download dart_snapshotter

mojo/public/mojo.gni

Index: mojo/public/mojo.gni
diff --git a/mojo/public/mojo.gni b/mojo/public/mojo.gni
index 2e2581400188d3a02c78d4c8249869244ae03e84..f32383e7035ab5897910a6037a0a99d67e9a48c9 100644
--- a/mojo/public/mojo.gni
+++ b/mojo/public/mojo.gni
@@ -12,6 +12,14 @@ if (!defined(mojo_build_mojo_shell_from_source) ||
   mojo_use_prebuilt_mojo_shell = is_linux || is_android
 }
 
+# If using the prebuilt dart_snapshotter, gate its usage by the platforms for
+# which it is published.
+mojo_use_prebuilt_dart_snapshotter = false
+if (!defined(mojo_build_dart_snapshotter_from_source) ||
+    !mojo_build_dart_snapshotter_from_source) {
+  mojo_use_prebuilt_dart_snapshotter = host_os == "linux" || host_os == "mac"

[jamesr, 2015/08/17 22:10:16]

what is a hypothetical developer on a different host_os supposed to do?  it
doesn't seem like they have any real choices - even if our prebuilts don't work
they certainly won't be able to build one themselves (i.e. the label won't
exist). i think what would make more sense here is to assert that the
module_args either set use_prebuilt_dart_snapshotter or specify a label for the
snapshot binary and not have branches on host_os

[zra, 2015/08/17 22:51:27]

Added assert that dart_snapshotter_bin is defined when we decide that
mojo_use_prebuilt_dart_snapshotter is false, which is when
mojo_build_dart_snapshotter_from_source is undefined or true.

+}
+
 # If using the prebuilt network service, gate its usage by the platforms for
 # which it is published.
 mojo_use_prebuilt_network_service = false