[Experimental Framework] Move the trial token public key out of content and into the embedder.

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 9d51d5ba83d4cf5a458f84137d963d39063c7c40..b4bef743bfb2043d3f5aa2786dd52e59d6dc2a0b 100644
--- a/content/public/common/content_client.h
+++ b/content/public/common/content_client.h
@@ -153,6 +153,10 @@ class CONTENT_EXPORT ContentClient {
   // model decisions.
   virtual bool IsSupplementarySiteIsolationModeEnabled();
 
+  // Returns the public key to be used for origin trials, or nullptr if origin
+  // trials are not enabled in this context.
+  virtual base::StringPiece GetOriginTrialPublicKey();
+
  private:
   friend class ContentClientInitializer;  // To set these pointers.
   friend class InternalTestInitializer;