Refactor embedded structures to top-level scope.

base/debug/activity_analyzer.h

Index: base/debug/activity_analyzer.h
diff --git a/base/debug/activity_analyzer.h b/base/debug/activity_analyzer.h
index 5333de29166ed2d039c82f35b63b89d65e518ce2..5a080b013ada9945055d779d2dd29c6cd65e369b 100644
--- a/base/debug/activity_analyzer.h
+++ b/base/debug/activity_analyzer.h
@@ -20,9 +20,6 @@ namespace debug {
 // makes that information available to other code.
 class BASE_EXPORT ThreadActivityAnalyzer {
  public:
-  using Activity = ThreadActivityTracker::Activity;
-  using ActivitySnapshot = ThreadActivityTracker::ActivitySnapshot;
-
   // This class provides keys that uniquely identify a thread, even across
   // multiple processes.
   class ThreadKey {