Fix newly discovered presubmit errors.

src/base/platform/platform.h

 // Copyright 2012 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.
 
 // This module contains the platform-specific code. This make the rest of the
 // code less dependent on operating system, compilers and runtime libraries.
 // This module does specifically not deal with differences between different
 // processor architecture.
 // The platform classes have the same definition for all platforms. The
 // implementation for a particular platform is put in platform_<os>.cc.
@@ skipping 410 matching lines @@
 // terminated.
 
 class Thread {
  public:
   // Opaque data type for thread-local storage keys.
   typedef int32_t LocalStorageKey;
 
   class Options {
    public:
     Options() : name_("v8:<unknown>"), stack_size_(0) {}
-    Options(const char* name, int stack_size = 0)
+    explicit Options(const char* name, int stack_size = 0)
         : name_(name), stack_size_(stack_size) {}
 
     const char* name() const { return name_; }
     int stack_size() const { return stack_size_; }
 
    private:
     const char* name_;
     int stack_size_;
   };
 
@@ skipping 75 matching lines @@
   char name_[kMaxThreadNameLength];
   int stack_size_;
   Semaphore* start_semaphore_;
 
   DISALLOW_COPY_AND_ASSIGN(Thread);
 };
 
 } }  // namespace v8::base
 
 #endif  // V8_BASE_PLATFORM_PLATFORM_H_