Make base::Environment::Create() return unique_ptrs.

base/environment.h

Index: base/environment.h
diff --git a/base/environment.h b/base/environment.h
index 12eeaf7ebb115ad0bd45d8c9e9cc64bbe180a161..3a4ed04e4bb58238dbe84708406ba4d8ce38e279 100644
--- a/base/environment.h
+++ b/base/environment.h
@@ -11,6 +11,7 @@
 
 #include "base/base_export.h"
 #include "base/strings/string16.h"
+#include "base/strings/string_piece.h"
 #include "build/build_config.h"
 
 namespace base {
@@ -27,23 +28,22 @@ class BASE_EXPORT Environment {
  public:
   virtual ~Environment();
 
-  // Static factory method that returns the implementation that provide the
-  // appropriate platform-specific instance.
-  static Environment* Create();
+  // Returns the appropriate platform-specific instance.
+  static std::unique_ptr<Environment> Create();
 
   // Gets an environment variable's value and stores it in |result|.
   // Returns false if the key is unset.
-  virtual bool GetVar(const char* variable_name, std::string* result) = 0;
+  virtual bool GetVar(StringPiece variable_name, std::string* result) = 0;
 
-  // Syntactic sugar for GetVar(variable_name, NULL);
-  virtual bool HasVar(const char* variable_name);
+  // Syntactic sugar for GetVar(variable_name, nullptr);
+  virtual bool HasVar(StringPiece variable_name);
 
   // Returns true on success, otherwise returns false.
-  virtual bool SetVar(const char* variable_name,
+  virtual bool SetVar(StringPiece variable_name,
                       const std::string& new_value) = 0;
 
   // Returns true on success, otherwise returns false.
-  virtual bool UnSetVar(const char* variable_name) = 0;
+  virtual bool UnSetVar(StringPiece variable_name) = 0;
 };