Add a content-security-policy (CSP) flag.

lib/compiler/implementation/dart2js.dart

Index: lib/compiler/implementation/dart2js.dart
diff --git a/lib/compiler/implementation/dart2js.dart b/lib/compiler/implementation/dart2js.dart
index 91e7b9290e33cff5865307865e65c3ab818c5890..a47dc476aa6cdac0c01493dc575ac65457f2c641 100644
--- a/lib/compiler/implementation/dart2js.dart
+++ b/lib/compiler/implementation/dart2js.dart
@@ -155,7 +155,8 @@ void compile(List<String> argv) {
     new OptionHandler('--enable-concrete-type-inference',
                       (_) => passThrough('--enable-concrete-type-inference')),
     new OptionHandler(r'--help|/\?|/h', (_) => wantHelp = true),
-    new OptionHandler(r'--package-root=.+|-p.+', setPackageRoot),
+    new OptionHandler('--package-root=.+|-p.+', setPackageRoot),
+    new OptionHandler('--enable-content-security-policy', passThrough),
     // The following two options must come last.
     new OptionHandler('-.*', (String argument) {
       helpAndFail('Error: Unknown option "$argument".');
@@ -392,7 +393,12 @@ be removed in a future version:
     libraries are used: dart:dom, dart:html dart:io.
 
   --enable-concrete-type-inference
-    Enable experimental concrete type inference.''');
+    Enable experimental concrete type inference.
+
+  --enable-content-security-policy
+    Emit JavaScript code that satisfies the CSP restrictions. This flag is
+    not continuously tested. Please report breakages and we will fix them
+    as soon as possible.''');
 }
 
 void helpAndExit(bool verbose) {