[Sync] Convert SyncSessionSnapshot to a copy-able class.

chrome/browser/sync/retry_verifier.h

Index: chrome/browser/sync/retry_verifier.h
diff --git a/chrome/browser/sync/retry_verifier.h b/chrome/browser/sync/retry_verifier.h
index 755dab9b0558582b0d1ef2f0a7ffafb5b85b4557..95023e227734a4f7bffd2cd1beb0a4d84777ec26 100644
--- a/chrome/browser/sync/retry_verifier.h
+++ b/chrome/browser/sync/retry_verifier.h
@@ -9,12 +9,11 @@
 #include "base/time.h"
 
 namespace browser_sync {
+
 namespace sessions {
-struct SyncSessionSnapshot;
+class SyncSessionSnapshot;
 }  // namespace sessions
-}  // namespace browser_sync
 
-namespace browser_sync {
 // The minimum and maximum wait times for a retry. The actual retry would take
 // place somewhere in this range. The algorithm that calculates the retry wait
 // time uses rand functions.
@@ -47,5 +46,7 @@ class RetryVerifier {
   bool done_;
   DISALLOW_COPY_AND_ASSIGN(RetryVerifier);
 };
+
 }  // namespace browser_sync
+
 #endif  // CHROME_BROWSER_SYNC_RETRY_VERIFIER_H_