Fix clang style warnings in webrtc/base

Mostly this consists of marking functions with override when
applicable, and moving function bodies from .h to .cc files.

Not inlining virtual functions with simple bodies such as

  { return false; }

strikes me as probably losing more in readability than we gain in
binary size and compilation time, but I guess it's just like any other
case where enabling a generally good warning forces us to write
slightly worse code in a couple of places.

BUG=163
R=kjellander@webrtc.org, tommi@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/47429004

Cr-Commit-Position: refs/heads/master@{#8656}
git-svn-id: http://webrtc.googlecode.com/svn/trunk@8656 4adac7df-926f-26a2-2b94-8c16560cd09d
diff --git a/webrtc/base/fileutils.cc b/webrtc/base/fileutils.cc
index 24375c9..6f385d7 100644
--- a/webrtc/base/fileutils.cc
+++ b/webrtc/base/fileutils.cc
@@ -148,6 +148,10 @@
   return default_filesystem_;
 }
 
+DirectoryIterator* FilesystemInterface::IterateDirectory() {
+  return new DirectoryIterator();
+}
+
 bool FilesystemInterface::CopyFolder(const Pathname &old_path,
                                      const Pathname &new_path) {
   bool success = true;
@@ -208,6 +212,10 @@
   return success;
 }
 
+bool FilesystemInterface::DeleteFolderAndContents(const Pathname& folder) {
+  return DeleteFolderContents(folder) && DeleteEmptyFolder(folder);
+}
+
 bool FilesystemInterface::CleanAppTempFolder() {
   Pathname path;
   if (!GetAppTempFolder(&path))