Add ProxyDecryptor which wraps concrete Decryptor implementations.

webkit/media/crypto/key_systems.cc

Index: webkit/media/crypto/key_systems.cc
diff --git a/webkit/media/key_systems.cc b/webkit/media/crypto/key_systems.cc
similarity index 96%
rename from webkit/media/key_systems.cc
rename to webkit/media/crypto/key_systems.cc
index 7efbb9ef9ff073340b4b6f028d2dd8f521507875..c606ea82359fb8ec13b5229d11028767fd4e823e 100644
--- a/webkit/media/key_systems.cc
+++ b/webkit/media/crypto/key_systems.cc
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include "webkit/media/key_systems.h"
+#include "webkit/media/crypto/key_systems.h"
 
 #include "third_party/WebKit/Source/WebKit/chromium/public/platform/WebString.h"
 
@@ -10,8 +10,6 @@ namespace webkit_media {
 
 namespace {
 
-const char kClearKeyKeySystem[] = "webkit-org.w3.clearkey";
-
 struct MediaFormatAndKeySystem {
   const char* mime_type;
   const char* codec;