[Extensions] Add allow-modals to the default sandbox CSP

chrome/common/extensions/manifest_tests/extension_manifests_sandboxed_unittest.cc

Index: chrome/common/extensions/manifest_tests/extension_manifests_sandboxed_unittest.cc
diff --git a/chrome/common/extensions/manifest_tests/extension_manifests_sandboxed_unittest.cc b/chrome/common/extensions/manifest_tests/extension_manifests_sandboxed_unittest.cc
index f0771d428cd90de8f4b08a76b1949a87582c8f1b..06b1425d5c179df90da27e231b37597ad66d31ee 100644
--- a/chrome/common/extensions/manifest_tests/extension_manifests_sandboxed_unittest.cc
+++ b/chrome/common/extensions/manifest_tests/extension_manifests_sandboxed_unittest.cc
@@ -35,7 +35,8 @@ TEST_F(SandboxedPagesManifestTest, SandboxedPages) {
   scoped_refptr<Extension> extension5(
       LoadAndExpectSuccess("sandboxed_pages_valid_5.json"));
 
-  const char kSandboxedCSP[] = "sandbox allow-scripts allow-forms allow-popups";
+  const char kSandboxedCSP[] =
+      "sandbox allow-scripts allow-forms allow-popups allow-modals";
   const char kDefaultCSP[] =
       "script-src 'self' blob: filesystem: chrome-extension-resource:; "
       "object-src 'self' blob: filesystem:;";