Remove 'String::append' from some of the blink source.

Source/modules/filesystem/DOMFilePath.cpp

 /*
  * Copyright (C) 2010 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 15 matching lines @@
  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #include "config.h"
 #include "modules/filesystem/DOMFilePath.h"
 
 #include "wtf/Vector.h"
 #include "wtf/text/CString.h"
+#include "wtf/text/StringBuilder.h"
 
 namespace WebCore {
 
 const char DOMFilePath::separator = '/';
 const char DOMFilePath::root[] = "/";
 
 String DOMFilePath::append(const String& base, const String& components)
 {
     return ensureDirectoryPath(base) + components;
 }
 
 String DOMFilePath::ensureDirectoryPath(const String& path)
 {
-    if (!DOMFilePath::endsWithSeparator(path)) {
-        String newPath = path;
-        newPath.append(DOMFilePath::separator);
-        return newPath;
-    }
+    if (!DOMFilePath::endsWithSeparator(path))
+        return path + DOMFilePath::separator;
     return path;
 }
 
 String DOMFilePath::getName(const String& path)
 {
     int index = path.reverseFind(DOMFilePath::separator);
     if (index != -1)
         return path.substring(index + 1);
     return path;
 }
@@ skipping 32 matching lines @@
             continue;
         if (components[i] == "..") {
             if (canonicalized.size() > 0)
                 canonicalized.removeLast();
             continue;
         }
         canonicalized.append(components[i]);
     }
     if (canonicalized.isEmpty())
         return DOMFilePath::root;
-    String result;
+    StringBuilder result;
     for (size_t i = 0; i < canonicalized.size(); ++i) {
         result.append(DOMFilePath::separator);
         result.append(canonicalized[i]);
     }
-    return result;
+    return result.toString();
 }
 
 bool DOMFilePath::isValidPath(const String& path)
 {
     if (path.isEmpty() || path == DOMFilePath::root)
         return true;
 
     // Embedded NULs are not allowed.
     if (path.find(static_cast<UChar>(0)) != WTF::kNotFound)
         return false;
@@ skipping 18 matching lines @@
 {
     if (name.isEmpty())
         return true;
     // '/' is not allowed in name.
     if (name.contains('/'))
         return false;
     return isValidPath(name);
 }
 
 } // namespace WebCore