Fix build error in ppapi_decryptor.cc

We were getting the following build error on Windows:

    FAILED: ninja -t msvc -o obj\webkit\media\crypto\webkit_media.ppapi_decryptor.obj -e environment.x86 -- cl.exe /nologo /showIncludes /FC @obj\webkit\media\crypto\webkit_media.ppapi_decryptor.obj.rsp /c ..\..\webkit\media\crypto\ppapi_decryptor.cc /Foobj\webkit\media\crypto\webkit_media.ppapi_decryptor.obj /Fdobj\webkit\support\webkit_media.pdb
    vendor\chromium\src\base\memory\ref_counted.h(250) : error C2027: use of undefined type 'webkit::ppapi::PPB_Buffer_Impl'

            vendor\chromium\src\webkit\plugins\ppapi\content_decryptor_delegate.h(30) : see declaration of 'webkit::ppapi::PPB_Buffer_Impl'

            vendor\chromium\src\base\memory\ref_counted.h(248) : while compiling class template member function 'scoped_refptr<T>::~scoped_refptr(void)'

            with

            [

                T=webkit::ppapi::PPB_Buffer_Impl

            ]

            vendor\chromium\src\webkit\plugins\ppapi\content_decryptor_delegate.h(163) : see reference to class template instantiation 'scoped_refptr<T>' being compiled

            with

            [

                T=webkit::ppapi::PPB_Buffer_Impl

            ]

    vendor\chromium\src\base\memory\ref_counted.h(250) : error C2227: left of '->Release' must point to class/struct/union/generic type

I believe something about our __declspec(dllexport) declarations is
causing this to happen. We work around this by defining an out-of-line
destructor for ContentDecryptorDelegate so ppapi_decryptor.cc doesn't
have to compile its destructor.

patches/content_decryptor_delegate.patch

@@ -0,0 +1,26 @@
+Index: webkit/plugins/ppapi/content_decryptor_delegate.cc
+===================================================================
+--- webkit/plugins/ppapi/content_decryptor_delegate.cc	(revision 194718)
++++ webkit/plugins/ppapi/content_decryptor_delegate.cc	(working copy)
+@@ -285,6 +285,9 @@
+       weak_this_(weak_ptr_factory_.GetWeakPtr()) {
+ }
+ 
++ContentDecryptorDelegate::~ContentDecryptorDelegate() {
++}
++
+ void ContentDecryptorDelegate::SetKeyEventCallbacks(
+     const media::KeyAddedCB& key_added_cb,
+     const media::KeyErrorCB& key_error_cb,
+Index: webkit/plugins/ppapi/content_decryptor_delegate.h
+===================================================================
+--- webkit/plugins/ppapi/content_decryptor_delegate.h	(revision 194718)
++++ webkit/plugins/ppapi/content_decryptor_delegate.h	(working copy)
+@@ -37,6 +37,7 @@
+   ContentDecryptorDelegate(
+       PP_Instance pp_instance,
+       const PPP_ContentDecryptor_Private* plugin_decryption_interface);
++  ~ContentDecryptorDelegate();
+ 
+   void SetKeyEventCallbacks(const media::KeyAddedCB& key_added_cb,
+                             const media::KeyErrorCB& key_error_cb,