Do not check webgpu handoff if not using webgpu

tfjs-core/src/io/io_utils.ts

@@ -27,6 +27,7 @@ import {Tensor} from '../tensor';
 import {backend} from '../globals';
 import {DataId} from '../tensor_info';
 import { env } from '../environment';
+import { getBackend } from '../globals';
 
 /** Number of bytes reserved for the length of the string. (32bit integer). */
 const NUM_BYTES_STRING_LENGTH = 4;
@@ -337,12 +338,15 @@ export async function decodeWeightsStream(
     tensors[spec.name] = weightTensor;
 
     // TODO(mattsoulanille): Better way to call uploadToGPU.
-    const b = backend();
     // TODO(mattsoulanille): Make this work for webgl too.
-    if ('uploadToGPU' in b &&
-      sizeFromShape(weightTensor.shape) >= (env()
-        .get('WEBGPU_CPU_HANDOFF_SIZE_THRESHOLD') as number)) {
-      (b.uploadToGPU as (dataId: DataId) => void)(weightTensor.dataId);
+    if (getBackend() === 'webgpu') {
+      const b = backend();
+
+      if ('uploadToGPU' in b &&
+        sizeFromShape(weightTensor.shape) >= (env()
+          .get('WEBGPU_CPU_HANDOFF_SIZE_THRESHOLD') as number)) {
+        (b.uploadToGPU as (dataId: DataId) => void)(weightTensor.dataId);
+      }
     }
   }