Add check if depth and stencil attachments are same image

gpu/command_buffer/service/framebuffer_manager.cc

Index: gpu/command_buffer/service/framebuffer_manager.cc
diff --git a/gpu/command_buffer/service/framebuffer_manager.cc b/gpu/command_buffer/service/framebuffer_manager.cc
index 0c5d96708e856d8e9c3d8578eb785c9f2d18c71e..4e06605d34966f1d89d25553105a5608ae95c25d 100644
--- a/gpu/command_buffer/service/framebuffer_manager.cc
+++ b/gpu/command_buffer/service/framebuffer_manager.cc
@@ -677,6 +677,25 @@ GLenum Framebuffer::IsPossiblyComplete(const FeatureInfo* feature_info) const {
     }
   }
 
+  // WebGL2 and GLES3 don't allow different images to bind to the depth and
+  // stencil attachment points, or GL_FRAMEBUFFER_UNSUPPORTED is returned.
+  if (feature_info->context_type() == CONTEXT_TYPE_WEBGL2 ||
+      feature_info->context_type() == CONTEXT_TYPE_OPENGLES3) {

[Zhenyao Mo, 2016/07/20 13:46:07]

We probably want to enforce this for all context types - even if it's es2
contexts, the underlying driver could still be es3, so it's better to just
enforce this.

+    AttachmentMap::const_iterator depth_it =
+        attachments_.find(GL_DEPTH_ATTACHMENT);
+    if (depth_it != attachments_.end()) {
+      AttachmentMap::const_iterator stencil_it =
+          attachments_.find(GL_STENCIL_ATTACHMENT);
+      if (stencil_it != attachments_.end()) {
+        if ((depth_it->second.get()->IsTextureAttachment() !=

[Zhenyao Mo, 2016/07/20 13:46:07]

This is incorrect.  First, you also need to consider renderbuffer situation. 
Second, just by comparing the object id does not guarantee it's the same image. 
In the case of 3d textures, you could bind two different layers.  In the case of
cube textures, you could bind two different faces.  In the case of 2d textures,
you could bind two different levels.  Please see
https://codereview.chromium.org/2159183002/ and use the function added in that
CL when it lands.

+             stencil_it->second.get()->IsTextureAttachment()) ||
+            (depth_it->second.get()->object_name() !=
+             stencil_it->second.get()->object_name())) {
+               return GL_FRAMEBUFFER_UNSUPPORTED;
+        }
+      }
+    }
+  }
   // This does not mean the framebuffer is actually complete. It just means our
   // checks passed.
   return GL_FRAMEBUFFER_COMPLETE;