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

gles/real_gles2_interface.cc

Index: gles/real_gles2_interface.cc
diff --git a/gles/real_gles2_interface.cc b/gles/real_gles2_interface.cc
index 954d169e539c553b756364545f31b9a497ae3cd6..1c5696c138d1843cc35dcc6e1b1b2e23e89badd8 100644
--- a/gles/real_gles2_interface.cc
+++ b/gles/real_gles2_interface.cc
@@ -249,6 +249,11 @@ void RealGles2Interface::DeleteTextures(GLsizei n, const GLuint* textures) {
   GLES2_DCHECK_ERROR();
 }
 
+void RealGles2Interface::DepthMask(GLboolean flag) {
+  glDepthMask(flag);
+  GLES2_DCHECK_ERROR();
+}
+
 void RealGles2Interface::Disable(GLenum cap) {
   glDisable(cap);
   GLES2_DCHECK_ERROR();