Enable creation of offscreen contexts which own their backing surface.

ui/gl/gl_surface.h

 // Copyright (c) 2012 The Chromium 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 UI_GL_GL_SURFACE_H_
 #define UI_GL_GL_SURFACE_H_
 
 #include <string>
 
 #include "base/callback.h"
@@ skipping 24 matching lines @@
 
 // Encapsulates a surface that can be rendered to with GL, hiding platform
 // specific management.
 class GL_EXPORT GLSurface : public base::RefCounted<GLSurface> {
  public:
   GLSurface();
 
   // Minimum bit depth of surface.
   enum Format {
     SURFACE_ARGB8888,
+    SURFACE_ARGB8888_DEPTH24,
     SURFACE_RGB565,
+    SURFACE_RGB565_DEPTH24,

[piman, 2016/11/16 00:44:02]

It seems like this won't scale to more depth bits or more surface formats.
We could either:
- explicitly add depth bits to GLSurface::Initialize
- change GLSurface::Initialize to take a GLSurfaceAttribs struct instead of
GLSurface::Format that can specify the color format, but also the depth and
stencil bits, MSAA samples, etc. over time as we need them.

[klausw, 2017/01/05 02:17:43]

See https://codereview.chromium.org/2616723002 for a new approach,
now using a GLSurfaceFormat class which replaces the custom format
types.

     SURFACE_OSMESA_BGRA,
     SURFACE_OSMESA_RGBA,
     SURFACE_SURFACELESS,
     SURFACE_DEFAULT = SURFACE_ARGB8888
   };
 
   // (Re)create the surface. TODO(apatrick): This is an ugly hack to allow the
   // EGL surface associated to be recreated without destroying the associated
   // context. The implementation of this function for other GLSurface derived
   // classes is in a pending changelist.
@@ skipping 239 matching lines @@
 
 // Wraps GLSurface in scoped_refptr and tries to initializes it. Returns a
 // scoped_refptr containing the initialized GLSurface or nullptr if
 // initialization fails.
 GL_EXPORT scoped_refptr<GLSurface> InitializeGLSurface(
     scoped_refptr<GLSurface> surface);
 
 }  // namespace gl
 
 #endif  // UI_GL_GL_SURFACE_H_