Bug 910412 - Filesystem API permission request and checks. r=dhylands

dom/filesystem/FileSystemUtils.cpp

@@ -47,6 +47,24 @@ FileSystemUtils::NormalizedPathToLocalPath(const nsAString& aNorm,
   aLocal = result;
 }
 
+// static
+bool
+FileSystemUtils::IsDescendantPath(const nsAString& aPath,
+                                  const nsAString& aDescendantPath)
+{
+  // The descendant path should begin with its ancestor path.
+  nsAutoString prefix;
+  prefix = aPath + NS_LITERAL_STRING(FILESYSTEM_DOM_PATH_SEPARATOR);
+
+  // Check the sub-directory path to see if it has the parent path as prefix.
+  if (aDescendantPath.Length() < prefix.Length() ||
+      !StringBeginsWith(aDescendantPath, prefix)) {
+    return false;
+  }
+
+  return true;
+}
+
 // static
 bool
 FileSystemUtils::IsParentProcess()