Don't show dart2js package warnings.

R=kevmoo@google.com

Review URL: https://codereview.chromium.org//1395223002 .
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 7a76650..aa737e7 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,9 @@
   schedule out-of-band asynchronous callbacks normally rather than having them
   throw exceptions.
 
+* Don't show package warnings when compiling tests with dart2js. This was
+  accidentally enabled in 0.12.2, but was never intended.
+
 ## 0.12.4+9
 
 * If a `tearDown()` callback throws an error, outer `tearDown()` callbacks are
diff --git a/lib/src/runner/browser/compiler_pool.dart b/lib/src/runner/browser/compiler_pool.dart
index edc41bf..54f51ea 100644
--- a/lib/src/runner/browser/compiler_pool.dart
+++ b/lib/src/runner/browser/compiler_pool.dart
@@ -71,7 +71,7 @@
         var dart2jsPath = p.join(sdkDir, 'bin', 'dart2js');
         if (Platform.isWindows) dart2jsPath += '.bat';
 
-        var args = ["--checked", wrapperPath, "--out=$jsPath", "--show-package-warnings"];
+        var args = ["--checked", wrapperPath, "--out=$jsPath"];
 
         if (packageRoot != null) {
           args.add("--package-root=${p.toUri(p.absolute(packageRoot))}");