glDiscardFramebuffer() in GrGpuGL::discard uses invalid GLenum

src/gpu/gl/GrGpuGL.cpp

Index: src/gpu/gl/GrGpuGL.cpp
diff --git a/src/gpu/gl/GrGpuGL.cpp b/src/gpu/gl/GrGpuGL.cpp
index b21043307016a6f0c2ee2a63163669f5c720bc5f..4c6f2fcaf194e4e27d565a4d7cc53205e24d8e14 100644
--- a/src/gpu/gl/GrGpuGL.cpp
+++ b/src/gpu/gl/GrGpuGL.cpp
@@ -1330,9 +1330,18 @@ void GrGpuGL::discard(GrRenderTarget* renderTarget) {
             }
             break;
         case GrGLCaps::kDiscard_InvalidateFBType: {
-            static const GrGLenum attachments[] = { GR_GL_COLOR };
-            GL_CALL(DiscardFramebuffer(GR_GL_FRAMEBUFFER, SK_ARRAY_COUNT(attachments),
-                    attachments));
+            if (0 == glRT->renderFBOID()) {
+                //  When rendering to the default framebuffer the legal values for attachments
+                //  are GL_COLOR, GL_DEPTH, GL_STENCIL, ... rather than the various FBO attachment
+                //  types. See glDiscardFramebuffer() spec.
+                static const GrGLenum attachments[] = { GR_GL_COLOR };
+                GL_CALL(DiscardFramebuffer(GR_GL_FRAMEBUFFER, SK_ARRAY_COUNT(attachments),
+                        attachments));
+            } else {
+                static const GrGLenum attachments[] = { GR_GL_COLOR_ATTACHMENT0 };
+                GL_CALL(DiscardFramebuffer(GR_GL_FRAMEBUFFER, SK_ARRAY_COUNT(attachments),
+                        attachments));
+            }
             break;
         }
     }