Add FilePath::FinalExtension and RemoveFinalExtension

base/files/file_path.h

Index: base/files/file_path.h
diff --git a/base/files/file_path.h b/base/files/file_path.h
index feb5f896687fa3e01bff31f006ef179b6919d799..54e0464ad57d61a4e5870fd817888f5a4ff76243 100644
--- a/base/files/file_path.h
+++ b/base/files/file_path.h
@@ -147,6 +147,12 @@ class FilePath {
   // A special path component meaning "this directory."
   static const CharType kCurrentDirectory[];
 
+  // A special path component meaning "the parent directory."
+  static const CharType kParentDirectory[];
+
+  // The character used to identify a file extension.
+  static const CharType kExtensionSeparator;
+
   FilePath();
   FilePath(const FilePath& that);
   explicit FilePath(const StringType& path);
@@ -184,6 +190,14 @@ class FilePath {
   // this is the only situation in which BaseName will return an absolute path.
   FilePath BaseName() const WARN_UNUSED_RESULT;
 
+  // Returns the path's file extension. This does not have a special case for
+  // common double extensions, so FinalExtension() of "foo.tar.gz" is simply
+  // "foo.tar".

[Mark Mentovai, 2015/01/20 17:11:53]

I think this comment means “.gz”, not “foo.tar”. RemoveFinalExtension() would be
“foo.tar”.

The comment should also say that extensionless paths will return "". The
upstream copy says so on Extension(), but since we’re not bringing Extension()
over, we should say so here.

[scottmg, 2015/01/20 18:01:27]

Done.

+  StringType FinalExtension() const;

[Mark Mentovai, 2015/01/20 17:11:53]

Even though upstream’s not WARN_UNUSED_RESULT, it should be, and this could be
here.

[scottmg, 2015/01/20 18:01:27]

I think generally only the FilePath returning ones are marked that way as in
that case it can be unclear if it's mutating or copying. But I guess there's no
useful reason to call FinalExtension() and ignore the result either.

+
+  // Returns a FilePath with FinalExtension() removed.
+  FilePath RemoveFinalExtension() const WARN_UNUSED_RESULT;
+
   // Returns a FilePath by appending a separator and the supplied path
   // component to this object's path.  Append takes care to avoid adding
   // excessive separators if this object's path already ends with a separator.