Stop polling for the query timer extension when the GPGPU context is disposed (#1352)
Stop polling for the query timer extension when the GPGPU context is disposed (#1352)

BUG Bail out of polling for the query timer if the context has been disposed
tensorflow/tfjs,tensorflow/tfjs-core,tensorflow/tfjs-core,tensorflow/tfjs,tensorflow/tfjs,tensorflow/tfjs-core,tensorflow/tfjs-core,tensorflow/tfjs,tensorflow/tfjs,tensorflow/tfjs,tensorflow/tfjs,tensorflow/tfjs-core,tensorflow/tfjs,tensorflow/tfjs-core,tensorflow/tfjs