first step for #168, adds dart:js impl to the build

tool/build_sdk.sh

Index: tool/build_sdk.sh
diff --git a/tool/build_sdk.sh b/tool/build_sdk.sh
index 9d5078ee981c6ce84edf316725092a1c650da1e5..7ef3710d7597aec085460fd4bb4a819fc124194e 100755
--- a/tool/build_sdk.sh
+++ b/tool/build_sdk.sh
@@ -14,7 +14,7 @@ fi
 
 # TODO(jmesserly): for now we're suppressing errors in SDK compilation
 dart -c bin/devc.dart --no-source-maps --sdk-check --force-compile -l warning \
-    --dart-sdk tool/generated_sdk -o lib/runtime/ dart:core \
+    --dart-sdk tool/generated_sdk -o lib/runtime/ dart:js \

[Jennifer Messerly, 2015/06/12 21:03:05]

JS includes core, so we still get it transitively.
We should support more than one source, though:
https://github.com/dart-lang/dev_compiler/issues/219

[Jacob, 2015/06/12 21:07:23]

make this a 
# comment in the shell script
having generate_sdk only build dart:js is a bit odd :)

[Jennifer Messerly, 2015/06/12 22:02:36]

haha. yes, good point.

     > tool/generated_sdk/sdk_errors.txt || true
 
 if [[ ! -f lib/runtime/dart/core.js ]] ; then