[CodeHealth] Remove calls to Value::GetAsDictionary (chrome/browser/platform_util_unittest.cc)

This CL takes removing GetAsDictionary as a starting point, but also
opportunistically migrates away from other deprecated base::Value APIs.

Bug: 1187011
Change-Id: I2d3152fee1b37cb085e17173a57d4580eaee861f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4054193
Reviewed-by: Yoichi Osato <[email protected]>
Commit-Queue: Vasilii Sukhanov <[email protected]>
Auto-Submit: Yoichi Osato <[email protected]>
Reviewed-by: Vasilii Sukhanov <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1075750}
diff --git a/chrome/browser/platform_util_unittest.cc b/chrome/browser/platform_util_unittest.cc
index ac28f24..9c1cd57 100644
--- a/chrome/browser/platform_util_unittest.cc
+++ b/chrome/browser/platform_util_unittest.cc
@@ -117,9 +117,7 @@
     JSONStringValueDeserializer json_string_deserializer(json_manifest);
     std::unique_ptr<base::Value> manifest =
         json_string_deserializer.Deserialize(&error_code, &error);
-    base::DictionaryValue* manifest_dictionary;
-
-    manifest->GetAsDictionary(&manifest_dictionary);
+    base::Value::Dict* manifest_dictionary = manifest->GetIfDict();
     ASSERT_TRUE(manifest_dictionary);
 
     scoped_refptr<extensions::Extension> extension =