Move AlterEnvironment to base/environment.h, implement on Windows.

base/environment.h

Index: base/environment.h
diff --git a/base/environment.h b/base/environment.h
index 5160ff2469f974786d089af4cc0dc07caa494b20..c8811e27eee354ccb6e4b80939327d3ffb622877 100644
--- a/base/environment.h
+++ b/base/environment.h
@@ -5,9 +5,12 @@
 #ifndef BASE_ENVIRONMENT_H_
 #define BASE_ENVIRONMENT_H_
 
+#include <map>
 #include <string>
 
 #include "base/base_export.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/strings/string16.h"
 #include "build/build_config.h"
 
 namespace base {
@@ -43,6 +46,45 @@ class BASE_EXPORT Environment {
   virtual bool UnSetVar(const char* variable_name) = 0;
 };
 
+
+#if defined(OS_WIN)
+
+typedef string16 NativeEnvironmentString;
+typedef std::map<NativeEnvironmentString, NativeEnvironmentString>
+    EnvironmentMap;
+
+// Returns a modified environment vector constructed from the given environment
+// and the list of changes given in |changes|. Each key in the environment is
+// matched against the first element of the pairs. In the event of a match, the
+// value is replaced by the second of the pair, unless the second is empty, in
+// which case the key-value is removed.
+//
+// This Windows version takes and returns a Windows-style environment block
+// which is a concatenated list of null-terminated 16-bit strings. The end is
+// marked by a double-null terminator. The size of the returned string will
+// include the terminators.
+BASE_EXPORT string16 AlterEnvironment(const wchar_t* env,
+                                      const EnvironmentMap& changes);
+
+#elif defined(OS_POSIX)
+
+typedef std::string NativeEnvironmentString;
+typedef std::map<NativeEnvironmentString, NativeEnvironmentString>
+    EnvironmentMap;
+
+// See general comments for the Windows version above.
+//
+// This Posix version takes and returns a Posix-style environment block, which
+// is a null-terminated list of pointers to null-terminated strings. The
+// returned array will have appended to it the storage for the array itself so
+// there is only one pointer to manage, but this means that you can't copy the
+// array without keeping the original around.
+BASE_EXPORT scoped_ptr<char*[]> AlterEnvironment(
+    const char* const* env,
+    const EnvironmentMap& changes);
+
+#endif
+
 }  // namespace base
 
 #endif  // BASE_ENVIRONMENT_H_