Extension content verification: new class for parsing data from store

extensions/test/data/content_verifier/payload.json

Index: extensions/test/data/content_verifier/payload.json
diff --git a/extensions/test/data/content_verifier/payload.json b/extensions/test/data/content_verifier/payload.json
new file mode 100644
index 0000000000000000000000000000000000000000..999506966602caf75bbd016fc242a7ef2f2ff787
--- /dev/null
+++ b/extensions/test/data/content_verifier/payload.json
@@ -0,0 +1,25 @@
+{
+  "content_hashes": [
+    {
+      "block_size": 4096,
+      "hash_block_size": 4096,
+      "format": "treehash",
+      "files": [
+        {
+          "path": "manifest.json",
+          "root_hash": "fafcb22089fb8920b383b5f7202508e7065aded1bbc3bbf2882724c5974919fb"
+        },
+        {
+          "path": "background.js",
+          "root_hash": "b711e21b9290bcda0f3921f915b428f596f9809db78f7a0507446ef433a7ce2c"
+        },
+        {
+          "path": "foo/bar.html",
+          "root_hash": "2f7ecb15b4ff866b7144bec07c664df584e95baca8cff662435a292c99f53595"
+        }
+      ]
+    }
+  ],
+  "item_id": "abcdefghijklmnopabcdefghijklmnop",
+  "item_version": "1.2.3"
+}