Pass in "mode" to transformer plugins.

sdk/lib/_internal/pub/lib/src/command/build.dart

Index: sdk/lib/_internal/pub/lib/src/command/build.dart
diff --git a/sdk/lib/_internal/pub/lib/src/command/build.dart b/sdk/lib/_internal/pub/lib/src/command/build.dart
index 93dee744ff5a0bf495623f626a3c640df9a94a0e..12dccf072c4d18ed0a85413d12f3ad74338a91e6 100644
--- a/sdk/lib/_internal/pub/lib/src/command/build.dart
+++ b/sdk/lib/_internal/pub/lib/src/command/build.dart
@@ -58,7 +58,8 @@ class BuildCommand extends PubCommand {
       // Since this server will only be hit by the transformer loader and isn't
       // user-facing, just use an IPv4 address to avoid a weird bug on the
       // OS X buildbots.
-      return barback.createServer("127.0.0.1", 0, graph,
+      // TODO(rnystrom): Allow specifying mode.

[nweiz, 2013/10/31 00:24:41]

We should make sure to do this before 1.0 so we don't have to support both
"--mode" and "--minify" forever.

[Bob Nystrom, 2013/10/31 01:51:19]

I'm not crazy about coupling minification to mode. I think users may want to
disable minification in pub build, or enable it in pub serve. I'm OK with that
flag sticking around for a good while.

[nweiz, 2013/10/31 18:47:56]

The question isn't whether you can disable minification in pub build -- it's
whether you can disable minification *and* enable release mode at the same time.
We don't have any evidence that users will want to do that. Even if they do
eventually, I don't think having a "--minify" flag is the right way to let users
configure dart2js separately from other transformers. We don't want to end up
adding pub flags for every option that could conceivably be passed to dart2js;
users should (eventually) configure it the same way they configure other
transformers.

Basically, the "--minify" flag provides no one any value now and won't be the
best way to support its use case in the future.

[Bob Nystrom, 2013/10/31 20:04:08]

OK, I'm fine with removing it, but I think that's out of scope for this patch.

From my discussion with Dan this morning, we don't plan to consider command-line
argument changes in tools breaking changes, so we can do this post 1.0 without
much difficulty.

+      return barback.createServer("127.0.0.1", 0, graph, BarbackMode.RELEASE,
           builtInTransformers: [dart2jsTransformer],
           watchForUpdates: false);
     }).then((server) {