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

content/shell/common/shell_content_client.h

Index: content/shell/common/shell_content_client.h
diff --git a/content/shell/common/shell_content_client.h b/content/shell/common/shell_content_client.h
index ceebc52d2bda93d34755b9524d490e0bdc720805..e0ddf0249f280a6d68b9abcfb41954cfa2610274 100644
--- a/content/shell/common/shell_content_client.h
+++ b/content/shell/common/shell_content_client.h
@@ -9,6 +9,7 @@
 #include <vector>
 
 #include "base/compiler_specific.h"
+#include "base/strings/string_piece.h"
 #include "content/public/common/content_client.h"
 
 namespace content {
@@ -17,6 +18,7 @@ std::string GetShellUserAgent();
 
 class ShellContentClient : public ContentClient {
  public:
+  ShellContentClient();
   ~ShellContentClient() override;
 
   std::string GetUserAgent() const override;
@@ -28,6 +30,11 @@ class ShellContentClient : public ContentClient {
       int resource_id) const override;
   gfx::Image& GetNativeImageNamed(int resource_id) const override;
   bool IsSupplementarySiteIsolationModeEnabled() override;
+
+  base::StringPiece GetOriginTrialPublicKey() override;
+
+ private:
+  base::StringPiece origin_trial_public_key_;
 };
 
 }  // namespace content