Misc. cleanup in grappler.

PiperOrigin-RevId: 256264467

tensorflow/core/grappler/clusters/virtual_cluster.h

@@ -33,11 +33,12 @@ namespace grappler {
 // actual graphs.
 class VirtualCluster : public Cluster {
  public:
-  VirtualCluster(const std::unordered_map<string, DeviceProperties>& devices);
+  explicit VirtualCluster(
+      const std::unordered_map<string, DeviceProperties>& devices);
   VirtualCluster(const std::unordered_map<string, DeviceProperties>& devices,
                  std::unique_ptr<OpLevelCostEstimator> node_estimator,
                  std::unique_ptr<ReadyNodeManager> node_manager);
-  VirtualCluster(const DeviceSet* device_set);
+  explicit VirtualCluster(const DeviceSet* device_set);
 
   ~VirtualCluster() override;
 

tensorflow/core/grappler/costs/robust_stats.h

@@ -21,8 +21,8 @@ namespace tensorflow {
 namespace grappler {
 class RobustStats {
  public:
-  RobustStats(const std::vector<double>& values);
-  RobustStats(std::vector<double>&& values);
+  explicit RobustStats(const std::vector<double>& values);
+  explicit RobustStats(std::vector<double>&& values);
 
   double lo() const { return lo_; }
   double hi() const { return hi_; }

tensorflow/core/grappler/costs/virtual_placer.h

@@ -30,7 +30,8 @@ class Cluster;
 // The virtual placer emulates the behavior of the TF placer.
 class VirtualPlacer {
  public:
-  VirtualPlacer(const std::unordered_map<string, DeviceProperties>& devices);
+  explicit VirtualPlacer(
+      const std::unordered_map<string, DeviceProperties>& devices);
 
   const DeviceProperties& get_device(const NodeDef& node) const;
 

tensorflow/core/grappler/optimizers/scoped_allocator_optimizer.h

@@ -25,8 +25,9 @@ limitations under the License.
 #include "tensorflow/core/protobuf/rewriter_config.pb.h"
 
 namespace tensorflow {
-namespace grappler {
 class Graph;
+
+namespace grappler {
 class GraphProperties;
 class NodeMap;
 class ScopedAllocatorOptimizer;