Add FilePath::FinalExtension() to avoid double extensions (.tar.gz) for file selector

base/files/file_path.cc

Index: base/files/file_path.cc
diff --git a/base/files/file_path.cc b/base/files/file_path.cc
index 4cfa2e650a9214e01aed42e55ecc6f067f8251fe..3ea5856a0d58c35c0abacb4b10fc87fd92379512 100644
--- a/base/files/file_path.cc
+++ b/base/files/file_path.cc
@@ -107,18 +107,21 @@ bool AreAllSeparators(const StringType& input) {
 
 // Find the position of the '.' that separates the extension from the rest
 // of the file name. The position is relative to BaseName(), not value().
-// This allows a second extension component of up to 4 characters when the
-// rightmost extension component is a common double extension (gz, bz2, Z).
-// For example, foo.tar.gz or foo.tar.Z would have extension components of
-// '.tar.gz' and '.tar.Z' respectively. Returns npos if it can't find an
-// extension.
-StringType::size_type ExtensionSeparatorPosition(const StringType& path) {
+// Returns npos if it can't find an extension.
+StringType::size_type FinalExtensionSeparatorPosition(const StringType& path) {
   // Special case "." and ".."
   if (path == FilePath::kCurrentDirectory || path == FilePath::kParentDirectory)
     return StringType::npos;
 
-  const StringType::size_type last_dot =
-      path.rfind(FilePath::kExtensionSeparator);
+  return path.rfind(FilePath::kExtensionSeparator);
+}
+
+// Same as above, but allow a second extension component of up to 4
+// characters when the rightmost extension component is a common double
+// extension (gz, bz2, Z).  For example, foo.tar.gz or foo.tar.Z would have
+// extension components of '.tar.gz' and '.tar.Z' respectively.
+StringType::size_type ExtensionSeparatorPosition(const StringType& path) {
+  const StringType::size_type last_dot = FinalExtensionSeparatorPosition(path);
 
   // No extension, or the extension is the whole filename.
   if (last_dot == StringType::npos || last_dot == 0U)
@@ -370,6 +373,15 @@ StringType FilePath::Extension() const {
   return base.path_.substr(dot, StringType::npos);
 }
 
+StringType FilePath::FinalExtension() const {
+  FilePath base(BaseName());
+  const StringType::size_type dot = FinalExtensionSeparatorPosition(base.path_);
+  if (dot == StringType::npos)
+    return StringType();
+
+  return base.path_.substr(dot, StringType::npos);
+}
+
 FilePath FilePath::RemoveExtension() const {
   if (Extension().empty())
     return *this;
@@ -381,6 +393,17 @@ FilePath FilePath::RemoveExtension() const {
   return FilePath(path_.substr(0, dot));
 }
 
+FilePath FilePath::RemoveFinalExtension() const {
+  if (FinalExtension().empty())
+    return *this;
+
+  const StringType::size_type dot = FinalExtensionSeparatorPosition(path_);
+  if (dot == StringType::npos)
+    return *this;
+
+  return FilePath(path_.substr(0, dot));
+}
+
 FilePath FilePath::InsertBeforeExtension(const StringType& suffix) const {
   if (suffix.empty())
     return FilePath(path_);