chrome: Cleanup class/struct forward declarations

chrome/app/chrome_crash_reporter_client.h

Index: chrome/app/chrome_crash_reporter_client.h
diff --git a/chrome/app/chrome_crash_reporter_client.h b/chrome/app/chrome_crash_reporter_client.h
index 6509f56022c3ae43e7185c3f45cd1ca0bfe68299..b6f256ff97721b4fa49852f717fb2ce472aba3c1 100644
--- a/chrome/app/chrome_crash_reporter_client.h
+++ b/chrome/app/chrome_crash_reporter_client.h
@@ -16,10 +16,6 @@
 #include "build/build_config.h"
 #include "components/crash/content/app/crash_reporter_client.h"
 
-namespace browser_watcher {
-class CrashReportingMetrics;
-}  // namespace browser_watcher
-
 class ChromeCrashReporterClient : public crash_reporter::CrashReporterClient {
  public:
   ChromeCrashReporterClient();