DOMStorageContextImpl that's implemented in terms of the new dom_storage classes.

webkit/dom_storage/dom_storage_area.cc

Index: webkit/dom_storage/dom_storage_area.cc
===================================================================
--- webkit/dom_storage/dom_storage_area.cc	(revision 127221)
+++ webkit/dom_storage/dom_storage_area.cc	(working copy)
@@ -16,6 +16,17 @@
 
 namespace dom_storage {
 
+// static
+const FilePath::CharType DomStorageArea::kDatabaseFileExtension[] =
+    FILE_PATH_LITERAL(".localstorage");
+
+// static
+FilePath DomStorageArea::DatabaseFileNameFromOrigin(const GURL& origin) {
+  std::string filename = fileapi::GetOriginIdentifierFromURL(origin);
+  return FilePath().Append(kDatabaseFileExtension).
+      InsertBeforeExtensionASCII(filename);

[jsbell, 2012/03/19 20:24:29]

As you note this is non-obvious; perhaps a comment: "filename looks like an
extension, so cannot use FilePath::ReplaceExtension"

... or just go ahead and add FilePath::AddExtension[ASCII]()

[michaeln, 2012/03/19 20:49:58]

Added a comment since i don't care to change the base library now and lengthen
the reveiw cycle for this minor detail.

+}
+
 DomStorageArea::DomStorageArea(
     int64 namespace_id, const GURL& origin,
     const FilePath& directory, DomStorageTaskRunner* task_runner)
@@ -164,11 +175,4 @@
   commit_in_flight_ = false;
 }
 
-// static
-FilePath DomStorageArea::DatabaseFileNameFromOrigin(const GURL& origin) {
-  std::string filename = fileapi::GetOriginIdentifierFromURL(origin)
-      + ".localstorage";
-  return FilePath().AppendASCII(filename);
-}
-
 }  // namespace dom_storage