Switch Safe Browsing's metadata from string to struct.

components/safe_browsing_db/safe_browsing_api_handler.h

Index: components/safe_browsing_db/safe_browsing_api_handler.h
diff --git a/components/safe_browsing_db/safe_browsing_api_handler.h b/components/safe_browsing_db/safe_browsing_api_handler.h
index 0ffdd6b5b6c0c51e88337595c51fd8004c8f2755..8ec5deb32a8c7e09a9b4af017d74be8d53d87257 100644
--- a/components/safe_browsing_db/safe_browsing_api_handler.h
+++ b/components/safe_browsing_db/safe_browsing_api_handler.h
@@ -24,13 +24,24 @@ class SafeBrowsingApiHandler {
   static SafeBrowsingApiHandler* GetInstance();
 
   typedef base::Callback<void(SBThreatType sb_threat_type,
-                              const std::string& metadata)>
+                              const ThreatMetadata& metadata)>
+      URLCheckCallbackMeta;
+
+  // TODO(nparker): Remove this as part of crbug/589610.
+  typedef base::Callback<void(SBThreatType sb_threat_type,
+                              const std::string& metadata_str)>
       URLCheckCallback;
 
   // Makes Native->Java call and invokes callback when check is done.
+  // TODO(nparker): Switch this back to pure virtual. crbug/589610.
+  virtual void StartURLCheck(const URLCheckCallbackMeta& callback,
+                             const GURL& url,
+                             const std::vector<SBThreatType>& threat_types);
+
+  // TODO(nparker): Remove this as part of crbug/589610.
   virtual void StartURLCheck(const URLCheckCallback& callback,
                              const GURL& url,
-                             const std::vector<SBThreatType>& threat_types) = 0;
+                             const std::vector<SBThreatType>& threat_types) {};
 
   virtual ~SafeBrowsingApiHandler() {}