cc: Add CopyResource function to ResourceProvider API.

cc/resources/resource_pool.h

Index: cc/resources/resource_pool.h
diff --git a/cc/resources/resource_pool.h b/cc/resources/resource_pool.h
index 8123152edd21df6c8834d2493174dec5280d3b01..5f481e986a1a86de14318eac7ad8ea3a40be3864 100644
--- a/cc/resources/resource_pool.h
+++ b/cc/resources/resource_pool.h
@@ -40,6 +40,7 @@ class CC_EXPORT ResourcePool {
   size_t acquired_memory_usage_bytes() const {
     return memory_usage_bytes_ - unused_memory_usage_bytes_;
   }
+  size_t total_resource_count() const { return resource_count_; }
   size_t acquired_resource_count() const {
     return resource_count_ - unused_resources_.size();
   }