Framebuffer: Fix getDepthStencilAttachment check.

The check should be using the newer operator== to check if attachments
are the same - the id() method will hit an UNREACHABLE if it's called
on a Surface attachment.

I noticed this when using this method in the Vulkan RenderPass
implementation.

BUG=angleproject:1583

Change-Id: I387b35805893d04003b22a1c7c9c12fc41c726ce
Reviewed-on: https://chromium-review.googlesource.com/412801
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>
diff --git a/src/libANGLE/Framebuffer.cpp b/src/libANGLE/Framebuffer.cpp
index 4bb2138..be0d601 100644
--- a/src/libANGLE/Framebuffer.cpp
+++ b/src/libANGLE/Framebuffer.cpp
@@ -151,8 +151,7 @@
     // A valid depth-stencil attachment has the same resource bound to both the
     // depth and stencil attachment points.
     if (mDepthAttachment.isAttached() && mStencilAttachment.isAttached() &&
-        mDepthAttachment.type() == mStencilAttachment.type() &&
-        mDepthAttachment.id() == mStencilAttachment.id())
+        mDepthAttachment == mStencilAttachment)
     {
         return &mDepthAttachment;
     }