Extension content verification: new class for parsing data from store

extensions/test/data/content_verifier/verified_contents.json

Index: extensions/test/data/content_verifier/verified_contents.json
diff --git a/extensions/test/data/content_verifier/verified_contents.json b/extensions/test/data/content_verifier/verified_contents.json
new file mode 100644
index 0000000000000000000000000000000000000000..ba86f3bac8c3fa1278e9b026ecfc20326bb5b93d
--- /dev/null
+++ b/extensions/test/data/content_verifier/verified_contents.json
@@ -0,0 +1,15 @@
+{
+  "payload": "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",
+  "signatures": [
+    {
+      "header": {"kid": "publisher"},
+      "protected": "eyJhbGciOiJSUzI1NiJ9",
+      "signature": "whatever"
+    },
+    {
+      "header": {"kid": "webstore"},
+      "protected": "eyJhbGciOiJSUzI1NiJ9",
+      "signature": "cLCoy+XfCahsNbF0xT6WBk2hvGwPut8D9mdkkKIDc6+wQVQryLSP2dGFqgS1XDP54vY8OqM8/7GrdTfVPim6aG80fAPd0YY3Q8nnn9zG2Lhr7rkYMMTdXFzE1bYamxoc3N9WNFkeisvXPZC26QX/D3JOlEisVhXym6DZRk3sibaVGh+mDgZej6YCzPQjnboquQsOsImL9Br7f3HxiH41kjMlsqX+PHrcgzeTVW5VOyiJVIEhOE1QDtgRPOW+MopaDPVvXxTsO8/LDeYE306CxVzemMJcKKaC39c2uOIn55cQqjOtPq1aqss7qFCSqGtvuMwmjSYEgV/q3VX/nc7npA"
+    }
+  ]
+}