FramebufferRenderbuffer() generates INVALID_OP if renderbuffer has never been bound.

third_party/WebKit/Source/modules/webgl/WebGLRenderingContextBase.cpp

Index: third_party/WebKit/Source/modules/webgl/WebGLRenderingContextBase.cpp
diff --git a/third_party/WebKit/Source/modules/webgl/WebGLRenderingContextBase.cpp b/third_party/WebKit/Source/modules/webgl/WebGLRenderingContextBase.cpp
index 3d05dca2b76522876991002f95137f0c932d7a91..0dfe7cf06037baf95da62d9bda336aac7d322fac 100644
--- a/third_party/WebKit/Source/modules/webgl/WebGLRenderingContextBase.cpp
+++ b/third_party/WebKit/Source/modules/webgl/WebGLRenderingContextBase.cpp
@@ -2519,9 +2519,10 @@ void WebGLRenderingContextBase::framebufferRenderbuffer(
                       "invalid target");
     return;
   }
-  if (buffer && !buffer->Validate(ContextGroup(), this)) {
+  if (buffer && (!buffer->HasEverBeenBound() ||
+                 !buffer->Validate(ContextGroup(), this))) {
     SynthesizeGLError(GL_INVALID_OPERATION, "framebufferRenderbuffer",
-                      "no buffer or buffer not from this context");
+                      "buffer never bound or buffer not from this context");
     return;
   }
   // Don't allow the default framebuffer to be mutated; all current