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

content/public/common/content_client.h

Index: content/public/common/content_client.h
diff --git a/content/public/common/content_client.h b/content/public/common/content_client.h
index f0862d5b40ac4d16b6bc2b3aa3d8b60f499455d2..5141bf8c153e7611ccfefb980fd843e9ee1da9b3 100644
--- a/content/public/common/content_client.h
+++ b/content/public/common/content_client.h
@@ -49,6 +49,7 @@ class ContentClient;
 class ContentGpuClient;
 class ContentRendererClient;
 class ContentUtilityClient;
+class OriginTrialPolicy;
 struct CdmInfo;
 struct PepperPluginInfo;
 
@@ -168,9 +169,9 @@ class CONTENT_EXPORT ContentClient {
   // model decisions.
   virtual bool IsSupplementarySiteIsolationModeEnabled();
 
-  // Returns the public key to be used for origin trials, or an empty string if
-  // origin trials are not enabled in this context.
-  virtual base::StringPiece GetOriginTrialPublicKey();
+  // Returns the origin trial policy, or nullptr if origin trials are not
+  // supported by the embedder.
+  virtual OriginTrialPolicy* GetOriginTrialPolicy();
 
 #if defined(OS_ANDROID)
   // Returns true for clients like Android WebView that uses synchronous