diff --git a/gpu/command_buffer/service/framebuffer_manager.cc b/gpu/command_buffer/service/framebuffer_manager.cc
index 9d0d0e3780442..056fccec70145 100644
--- a/gpu/command_buffer/service/framebuffer_manager.cc
+++ b/gpu/command_buffer/service/framebuffer_manager.cc
@@ -467,6 +467,21 @@ void Framebuffer::ClearUnclearedIntRenderbufferAttachments(
       DCHECK_GT(GL_COLOR_ATTACHMENT0 + manager_->max_draw_buffers_,
                 attaching_point);
       GLint drawbuffer = it->first - GL_COLOR_ATTACHMENT0;
+      // POC INSTRUMENTATION: log the actual DRAW_BUFFERi state so we can
+      // observe whether glClearBuffer*iv targets a NONE draw buffer (no-op).
+      {
+        GLint cur_draw_buf = -1;
+        glGetIntegerv(GL_DRAW_BUFFER0 + drawbuffer, &cur_draw_buf);
+        LOG(ERROR) << "[POC] ClearUnclearedIntRenderbufferAttachments: "
+                   << "attachment=COLOR_ATTACHMENT" << drawbuffer
+                   << " glClearBuffer*iv(GL_COLOR, " << drawbuffer << ", 0)"
+                   << " DRAW_BUFFER" << drawbuffer << "=0x" << std::hex
+                   << cur_draw_buf << std::dec
+                   << (cur_draw_buf == GL_NONE
+                           ? " (GL_NONE -> CLEAR IS NO-OP, but SetCleared(true)"
+                             " runs => UNINITIALIZED DATA DISCLOSURE)"
+                           : "");
+      }
       if (GLES2Util::IsUnsignedIntegerFormat(internal_format)) {
         const GLuint kZero[] = { 0u, 0u, 0u, 0u };
         glClearBufferuiv(GL_COLOR, drawbuffer, kZero);