Fixing allow_csp_from.html test and enabling it back in sit-per-process

third_party/WebKit/LayoutTests/http/tests/security/contentSecurityPolicy/resources/child-csp-test.js

Index: third_party/WebKit/LayoutTests/http/tests/security/contentSecurityPolicy/resources/child-csp-test.js
diff --git a/third_party/WebKit/LayoutTests/http/tests/security/contentSecurityPolicy/resources/child-csp-test.js b/third_party/WebKit/LayoutTests/http/tests/security/contentSecurityPolicy/resources/child-csp-test.js
index 77f8228d9027d4364fa537468ec1592648fbc95c..87d131252e0a7ebadb360743bdfd066994059f4b 100644
--- a/third_party/WebKit/LayoutTests/http/tests/security/contentSecurityPolicy/resources/child-csp-test.js
+++ b/third_party/WebKit/LayoutTests/http/tests/security/contentSecurityPolicy/resources/child-csp-test.js
@@ -21,7 +21,11 @@ function injectIframeWithCSP(url, shouldBlock, csp, t, urlId) {
     });
 
     if (shouldBlock) {
-        window.onmessage = t.unreached_func('No message should be sent from the frame.');
+        window.onmessage = function (e) {
+            if (e.source != i.contentWindow)
+                return;
+            t.unreached_func('No message should be sent from the frame.');
+        }
         i.onload = t.step_func(function () {
             // Delay the check until after the postMessage has a chance to execute.
             setTimeout(t.step_func_done(function () {