Fix creating target paths in file_util_posix CopyDirectory.

base/file_util_posix.cc

Index: base/file_util_posix.cc
diff --git a/base/file_util_posix.cc b/base/file_util_posix.cc
index 0ffa6247a2f048b8039161d8eaf56e9d55097505..49cf873186d783a5251cf75fff7b45f9e6eb61de 100644
--- a/base/file_util_posix.cc
+++ b/base/file_util_posix.cc
@@ -343,15 +343,15 @@ bool CopyDirectory(const FilePath& from_path,
   DCHECK(recursive || S_ISDIR(info.stat.st_mode));
 
   while (success && !current.empty()) {
-    // current is the source path, including from_path, so paste
-    // the suffix after from_path onto to_path to create the target_path.
-    std::string suffix(&current.value().c_str()[from_path_base.value().size()]);
-    // Strip the leading '/' (if any).
-    if (!suffix.empty()) {
-      DCHECK_EQ('/', suffix[0]);
-      suffix.erase(0, 1);
+    // current is the source path, including from_path, so append
+    // the suffix after from_path to to_path to create the target_path.
+    FilePath target_path(to_path);
+    if (from_path_base != current) {
+      if (!from_path_base.AppendRelativePath(current, &target_path)) {
+        success = false;
+        break;
+      }
     }
-    const FilePath target_path = to_path.Append(suffix);
 
     if (S_ISDIR(info.stat.st_mode)) {
       if (mkdir(target_path.value().c_str(), info.stat.st_mode & 01777) != 0 &&