wm: Add two pass rendering to OpenGL|ES backend.

gles/real_gles2_interface.h

 // Copyright (c) 2010 The Chromium OS Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef WINDOW_MANAGER_REAL_GLES2_INTERFACE_H_
 #define WINDOW_MANAGER_REAL_GLES2_INTERFACE_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 52 matching lines @@
   void Clear(GLbitfield mask);
   void ClearColor(GLclampf red, GLclampf green, GLclampf blue,
                   GLclampf alpha);
   void CompileShader(GLuint shader);
   GLuint CreateProgram();
   GLuint CreateShader(GLenum type);
   void DeleteBuffers(GLsizei n, const GLuint* buffers);
   void DeleteProgram(GLuint program);
   void DeleteShader(GLuint shader);
   void DeleteTextures(GLsizei n, const GLuint* textures);
+  void DepthMask(GLboolean flag);
   void Disable(GLenum cap);
   void DisableVertexAttribArray(GLuint index);
   void DrawArrays(GLenum mode, GLint first, GLsizei count);
   void Enable(GLenum cap);
   void EnableVertexAttribArray(GLuint index);
   void GenBuffers(GLsizei n, GLuint* buffers);
   void GenTextures(GLsizei n, GLuint* textures);
   int GetAttribLocation(GLuint program, const char* name);
   GLenum GetError();
   void GetIntegerv(GLenum pname, GLint* params);
@@ skipping 62 matching lines @@
       gl_egl_image_target_texture_2d_oes_;
   PFNGLEGLIMAGETARGETRENDERBUFFERSTORAGEOESPROC
       gl_egl_image_target_renderbuffer_storage_oes_;
 
   DISALLOW_COPY_AND_ASSIGN(RealGles2Interface);
 };
 
 }  // namespace window_manager
 
 #endif