Generate INVALID_OPERATION if feedback loops exist in CopyTex{Sub}Image2D.

gpu/command_buffer/service/framebuffer_manager.cc

Index: gpu/command_buffer/service/framebuffer_manager.cc
diff --git a/gpu/command_buffer/service/framebuffer_manager.cc b/gpu/command_buffer/service/framebuffer_manager.cc
index 4448ac8a86d038f422d30de346888978cbef4fc9..60f3ac97a8236322d700e94f4a57431dffd51410 100644
--- a/gpu/command_buffer/service/framebuffer_manager.cc
+++ b/gpu/command_buffer/service/framebuffer_manager.cc
@@ -126,6 +126,10 @@ class RenderbufferAttachment
 
   virtual void OnWillRenderTo() const override {}
   virtual void OnDidRenderTo() const override {}
+  virtual bool FormsFeedbackLoop(
+      TextureRef* /* texture */, GLint /*level */) const override {
+    return false;
+  }
 
  protected:
   virtual ~RenderbufferAttachment() { }
@@ -264,6 +268,11 @@ class TextureAttachment
     texture_ref_->texture()->OnDidModifyPixels();
   }
 
+  virtual bool FormsFeedbackLoop(
+      TextureRef* texture, GLint level) const override {
+    return texture == texture_ref_.get() && level == level_;
+  }
+
  protected:
   virtual ~TextureAttachment() {}