Make Dart heap size bigger when running pub.

sdk/bin/pub

Index: sdk/bin/pub
diff --git a/sdk/bin/pub b/sdk/bin/pub
index 231da3ebc4cbc2580e647e355e622608a6fa7ab5..6f5612107afe5a18df2779004e0f5de606285b32 100755
--- a/sdk/bin/pub
+++ b/sdk/bin/pub
@@ -12,12 +12,16 @@
 BIN_DIR="$(cd "${0%/*}" ; pwd -P)"
 SDK_DIR="$(cd "${BIN_DIR}/.." ; pwd -P)"
 
+# Increase the heap size for Dart. Pub runs dart2js, which uses a lot of
+# memory.
+DART_FLAGS="--new_gen_heap_size=256 --old_gen_heap_size=1536"
+
 SNAPSHOT="$BIN_DIR/snapshots/pub.dart.snapshot"
 
 if test -f "$SNAPSHOT"; then
   # We are running the snapshot in the built SDK.
   DART="$BIN_DIR/dart"
-  exec "$DART" "$SNAPSHOT" "$@"
+  exec "$DART" "$DART_FLAGS" "$SNAPSHOT" "$@"
 else
   # We are running pub from source in the development repo.
   if [ -z "$DART_CONFIGURATION" ];
@@ -39,5 +43,5 @@ else
 
   PUB="$SDK_DIR/lib/_internal/pub/bin/pub.dart"
 
-  exec "$DART" "--package-root=$PACKAGES_DIR" "$PUB" "$@"
+  exec "$DART" "$DART_FLAGS" "--package-root=$PACKAGES_DIR" "$PUB" "$@"
 fi