WebGL compatibility: add stencil mask and ref restriction

BUG=angleproject:1523
BUG=chromium:668223

Change-Id: I0726769c938fdfd50af0fad1cef1746d4af2a589
Reviewed-on: https://chromium-review.googlesource.com/422084
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
diff --git a/src/libANGLE/Framebuffer.h b/src/libANGLE/Framebuffer.h
index db0d621..bdc7a30 100644
--- a/src/libANGLE/Framebuffer.h
+++ b/src/libANGLE/Framebuffer.h
@@ -62,6 +62,7 @@
     const FramebufferAttachment *getReadAttachment() const;
     const FramebufferAttachment *getFirstColorAttachment() const;
     const FramebufferAttachment *getDepthOrStencilAttachment() const;
+    const FramebufferAttachment *getStencilOrDepthStencilAttachment() const;
     const FramebufferAttachment *getColorAttachment(size_t colorAttachment) const;
     const FramebufferAttachment *getDepthAttachment() const;
     const FramebufferAttachment *getStencilAttachment() const;
@@ -121,6 +122,7 @@
     const FramebufferAttachment *getStencilbuffer() const;
     const FramebufferAttachment *getDepthStencilBuffer() const;
     const FramebufferAttachment *getDepthOrStencilbuffer() const;
+    const FramebufferAttachment *getStencilOrDepthStencilAttachment() const;
     const FramebufferAttachment *getReadColorbuffer() const;
     GLenum getReadColorbufferType() const;
     const FramebufferAttachment *getFirstColorbuffer() const;