c/b/safe_browsing/certificate_reporting_service_factory.h: add forward declaration for base::Clock

Change-Id: If6d42457b8d40040ef09695eaf8197b06fd99575
Reviewed-on: https://chromium-review.googlesource.com/967322
Commit-Queue: Nathan Parker <nparker@chromium.org>
Reviewed-by: Nathan Parker <nparker@chromium.org>
Cr-Commit-Position: refs/heads/master@{#545631}

chrome/browser/safe_browsing/certificate_reporting_service_factory.h

@@ -8,6 +8,10 @@
 #include "base/memory/singleton.h"
 #include "components/keyed_service/content/browser_context_keyed_service_factory.h"
 
+namespace base {
+class Clock;
+}
+
 namespace content {
 class BrowserContext;
 }