Refactor OriginTrialPolicy to be an abstract interface in content/public/common

content/public/common/content_client.cc

Index: content/public/common/content_client.cc
diff --git a/content/public/common/content_client.cc b/content/public/common/content_client.cc
index 4deed2d832cb07efa90df369c513cb16386df55a..202a828a98eba51714b6f66ae88bd44d25c03944 100644
--- a/content/public/common/content_client.cc
+++ b/content/public/common/content_client.cc
@@ -119,8 +119,10 @@ bool ContentClient::IsSupplementarySiteIsolationModeEnabled() {
   return false;
 }
 
-base::StringPiece ContentClient::GetOriginTrialPublicKey() {
-  return base::StringPiece();
+void ContentClient::InitializeOriginTrialPolicy() {}
+
+const OriginTrialPolicy* ContentClient::GetOriginTrialPolicy() const {
+  return nullptr;
 }
 
 bool ContentClient::AllowScriptExtensionForServiceWorker(