Precache manifest should not be added to fetcher pool which is full

components/precache/core/fetcher_pool.h

Index: components/precache/core/fetcher_pool.h
diff --git a/components/precache/core/fetcher_pool.h b/components/precache/core/fetcher_pool.h
index 2be36e28f508346e8e6529c40022991e95a4c32a..c6a46543b5ee6bee204e0f6b6edd829f699287bb 100644
--- a/components/precache/core/fetcher_pool.h
+++ b/components/precache/core/fetcher_pool.h
@@ -8,6 +8,7 @@
 #include <memory>
 #include <unordered_map>
 
+#include "base/gtest_prod_util.h"
 #include "base/logging.h"
 
 namespace precache {
@@ -71,6 +72,9 @@ class FetcherPool {
     return elements_;
   }
 
+  // Returns the maximum size of the pool.
+  size_t max_size() const { return max_size_; }
+
  private:
   const size_t max_size_;
   std::unordered_map<const T*, std::unique_ptr<T>> elements_;