Make some FramebufferAttachment methods const.

BUG=angle:841

Change-Id: I4670e417c1976ebd2198ea4c8927a00fff7bb15c
Reviewed-on: https://chromium-review.googlesource.com/232380
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Tested-by: Geoff Lang <geofflang@chromium.org>
diff --git a/src/libANGLE/FramebufferAttachment.cpp b/src/libANGLE/FramebufferAttachment.cpp
index f47875f..2fa9b0b 100644
--- a/src/libANGLE/FramebufferAttachment.cpp
+++ b/src/libANGLE/FramebufferAttachment.cpp
@@ -136,7 +136,7 @@
     return mIndex.layerIndex;
 }
 
-Texture *TextureAttachment::getTexture()
+Texture *TextureAttachment::getTexture() const
 {
     return mTexture.get();
 }
@@ -146,7 +146,7 @@
     return &mIndex;
 }
 
-Renderbuffer *TextureAttachment::getRenderbuffer()
+Renderbuffer *TextureAttachment::getRenderbuffer() const
 {
     UNREACHABLE();
     return NULL;
@@ -216,7 +216,7 @@
     return 0;
 }
 
-Texture *RenderbufferAttachment::getTexture()
+Texture *RenderbufferAttachment::getTexture() const
 {
     UNREACHABLE();
     return NULL;
@@ -228,7 +228,7 @@
     return NULL;
 }
 
-Renderbuffer *RenderbufferAttachment::getRenderbuffer()
+Renderbuffer *RenderbufferAttachment::getRenderbuffer() const
 {
     return mRenderbuffer.get();
 }
@@ -296,7 +296,7 @@
     return 0;
 }
 
-Texture *DefaultAttachment::getTexture()
+Texture *DefaultAttachment::getTexture() const
 {
     UNREACHABLE();
     return NULL;
@@ -308,7 +308,7 @@
     return NULL;
 }
 
-Renderbuffer *DefaultAttachment::getRenderbuffer()
+Renderbuffer *DefaultAttachment::getRenderbuffer() const
 {
     UNREACHABLE();
     return NULL;