[WebNN] Fixes MLTensor caching across different contexts (microsoft#2…

…3100)

We weren't checking that MLTensors were from the same context before
reusing them.

Found while debugging microsoft/webnn-developer-preview#69

js/web/lib/wasm/jsep/webnn/tensor-manager.ts

@@ -141,8 +141,9 @@ class TensorWrapper {
     return this.mlContext.readTensor(this.mlTensor);
   }
 
-  public sameTypeAndShape(dataType: MLOperandDataType, shape: readonly number[]): boolean {
+  public canReuseTensor(context: MLContext, dataType: MLOperandDataType, shape: readonly number[]): boolean {
     return (
+      this.mlContext === context &&
       this.dataType === dataType &&
       this.tensorShape.length === shape.length &&
       this.tensorShape.every((v, i) => v === shape[i])
@@ -176,12 +177,13 @@ class TensorIdTracker {
   }
 
   public async ensureTensor(
+    context: MLContext,
     dataType: MLOperandDataType,
     shape: readonly number[],
     copyOld: boolean,
   ): Promise<MLTensor> {
     if (this.wrapper) {
-      if (this.wrapper.sameTypeAndShape(dataType, shape)) {
+      if (this.wrapper.canReuseTensor(context, dataType, shape)) {
         return this.wrapper.tensor;
       } else {
         if (copyOld) {
@@ -288,7 +290,7 @@ class TensorManagerImpl implements TensorManager {
     if (!tensor) {
       throw new Error('Tensor not found.');
     }
-    return tensor.ensureTensor(dataType, shape, copyOld);
+    return tensor.ensureTensor(this.backend.currentContext, dataType, shape, copyOld);
   }
 
   public upload(tensorId: TensorId, data: Uint8Array): void {
@@ -354,15 +356,15 @@ class TensorManagerImpl implements TensorManager {
     readable: boolean,
   ): Promise<TensorWrapper> {
     const sessionId = this.backend.currentSessionId;
+    const context = this.backend.currentContext;
     for (const [index, tensor] of this.freeTensors.entries()) {
-      if (tensor.sameTypeAndShape(dataType, shape)) {
+      if (tensor.canReuseTensor(context, dataType, shape)) {
         LOG_DEBUG('verbose', () => `[WebNN] Reusing tensor {dataType: ${dataType}, shape: ${shape}}`);
         const wrapper = this.freeTensors.splice(index, 1)[0];
         wrapper.sessionId = sessionId;
         return wrapper;
       }
     }
-    const context = this.backend.currentContext;
     LOG_DEBUG('verbose', () => `[WebNN] MLContext.createTensor {dataType: ${dataType}, shape: ${shape}}`);
     const tensor = await context.createTensor({
       dataType,