Don't run pub in checked mode in the built SDK.

sdk/bin/pub

Index: sdk/bin/pub
diff --git a/sdk/bin/pub b/sdk/bin/pub
index 364308575a70b78b474370ad71ba9da071876103..231da3ebc4cbc2580e647e355e622608a6fa7ab5 100755
--- a/sdk/bin/pub
+++ b/sdk/bin/pub
@@ -17,7 +17,7 @@ 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" "--checked" "$SNAPSHOT" "$@"
+  exec "$DART" "$SNAPSHOT" "$@"
 else
   # We are running pub from source in the development repo.
   if [ -z "$DART_CONFIGURATION" ];
@@ -39,5 +39,5 @@ else
 
   PUB="$SDK_DIR/lib/_internal/pub/bin/pub.dart"
 
-  exec "$DART" "--checked" "--package-root=$PACKAGES_DIR" "$PUB" "$@"
+  exec "$DART" "--package-root=$PACKAGES_DIR" "$PUB" "$@"
 fi