Split Dictionary's get and convert into DictionaryHelper.

Source/modules/crypto/SubtleCrypto.cpp

Index: Source/modules/crypto/SubtleCrypto.cpp
diff --git a/Source/modules/crypto/SubtleCrypto.cpp b/Source/modules/crypto/SubtleCrypto.cpp
index dcde256deb0ddf1ac8b28c54ca08141e145c3728..e1ed70ee7ee55efb795ca217996c61d943f3b064 100644
--- a/Source/modules/crypto/SubtleCrypto.cpp
+++ b/Source/modules/crypto/SubtleCrypto.cpp
@@ -140,7 +140,7 @@ static ScriptPromise startCryptoOperation(ScriptState* scriptState, const Dictio
 static bool copyStringProperty(const char* property, const Dictionary& source, JSONObject* destination)
 {
     String value;
-    if (!source.get(property, value))
+    if (!DictionaryHelper::get(source, property, value))
         return false;
     destination->setString(property, value);
     return true;
@@ -149,7 +149,7 @@ static bool copyStringProperty(const char* property, const Dictionary& source, J
 static bool copySequenceOfStringProperty(const char* property, const Dictionary& source, JSONObject* destination)
 {
     Vector<String> value;
-    if (!source.get(property, value))
+    if (!DictionaryHelper::get(source, property, value))
         return false;
     RefPtr<JSONArray> jsonArray = JSONArray::create();
     for (unsigned i = 0; i < value.size(); ++i)
@@ -176,7 +176,7 @@ static bool copyJwkDictionaryToJson(const Dictionary& dict, CString& jsonUtf8, C
     copyStringProperty("alg", dict, jsonObject.get());
 
     bool ext;
-    if (dict.get("ext", ext))
+    if (DictionaryHelper::get(dict, "ext", ext))
         jsonObject->setBoolean("ext", ext);
 
     const char* const propertyNames[] = { "d", "n", "e", "p", "q", "dp", "dq", "qi", "k" };