Fix newly discovered presubmit errors.

src/hydrogen.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/hydrogen.h"
 
 #include <algorithm>
 
 #include "src/v8.h"
 
@@ skipping 7421 matching lines @@
     return NewArgumentAdaptorCall(target, context,
         argument_count, param_count_value);
   }
   UNREACHABLE();
   return NULL;
 }
 
 
 class FunctionSorter {
  public:
-  FunctionSorter(int index = 0, int ticks = 0, int size = 0)
-      : index_(index), ticks_(ticks), size_(size) { }
+  explicit FunctionSorter(int index = 0, int ticks = 0, int size = 0)
+      : index_(index), ticks_(ticks), size_(size) {}
 
   int index() const { return index_; }
   int ticks() const { return ticks_; }
   int size() const { return size_; }
 
  private:
   int index_;
   int ticks_;
   int size_;
 };
@@ skipping 5027 matching lines @@
   if (ShouldProduceTraceOutput()) {
     isolate()->GetHTracer()->TraceHydrogen(name(), graph_);
   }
 
 #ifdef DEBUG
   graph_->Verify(false);  // No full verify.
 #endif
 }
 
 } }  // namespace v8::internal