Mark --disallow-unsafe-eval as a supported feature in usage description.

sdk/lib/_internal/compiler/implementation/dart2js.dart

Index: sdk/lib/_internal/compiler/implementation/dart2js.dart
diff --git a/sdk/lib/_internal/compiler/implementation/dart2js.dart b/sdk/lib/_internal/compiler/implementation/dart2js.dart
index c74068e49a82c04789b3336a612f83a276a04136..c76c45f1a4a176adf1db478c5276e4c81f8e2fbe 100644
--- a/sdk/lib/_internal/compiler/implementation/dart2js.dart
+++ b/sdk/lib/_internal/compiler/implementation/dart2js.dart
@@ -406,6 +406,10 @@ Supported options:
   --minify
     Generate minified output.
 
+  --disallow-unsafe-eval
+    Disable dynamic generation of code in the generated output. This is
+    necessary to satisfy CSP restrictions (see http://www.w3.org/TR/CSP/).
+
   --suppress-warnings
     Do not display any warnings.
 
@@ -435,12 +439,6 @@ be removed in a future version:
     Disable the optimization that removes unused native types from dart:html
     and related libraries.
 
-  --disallow-unsafe-eval
-    Disable dynamic generation of code in the generated output. This is
-    necessary to satisfy CSP restrictions (see http://www.w3.org/TR/CSP/).
-    This flag is not continuously tested. Please report breakages and we
-    will fix them as soon as possible.
-
   --reject-deprecated-language-features
     Reject deprecated language features.  Without this option, the
     compiler will accept language features that are no longer valid