Check if precaching is allowed before reporting related metrics

components/precache/content/precache_manager.h

Index: components/precache/content/precache_manager.h
diff --git a/components/precache/content/precache_manager.h b/components/precache/content/precache_manager.h
index 552af2a2a59a302b4fd2dd03e6190322c786e942..e274881508a0a1bad480de0e72856e92574dd581 100644
--- a/components/precache/content/precache_manager.h
+++ b/components/precache/content/precache_manager.h
@@ -49,6 +49,9 @@ class PrecacheManager : public KeyedService,
   // command line flag. This method can be called on any thread.
   static bool IsPrecachingEnabled();
 
+  // Returns true if precaching is allowed for the browser context.
+  bool IsPrecachingAllowed();
+
   // Starts precaching resources that the user is predicted to fetch in the
   // future. If precaching is already currently in progress, then this method
   // does nothing. The |precache_completion_callback| will be run when