[WebGPU] Add FlexibleArrayBufferView to GPUBuffer.setSubData src

FlexibleArrayBufferView allows small ArrayBufferViews to be passed as a
temporary on the stack. This saves creating global handles and weak
roots in V8.

Bug: 852089
Change-Id: Ic0e8ee941c5175ac5232d5b6a2c1f3f1a315bf9e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1894409Reviewed-by: Kai Ninomiya <kainino@chromium.org>
Commit-Queue: Austin Eng <enga@chromium.org>
Cr-Commit-Position: refs/heads/master@{#711593}

third_party/blink/renderer/modules/webgpu/gpu_buffer.cc

@@ -128,13 +128,13 @@ void GPUBuffer::Trace(blink::Visitor* visitor) {
 }
 
 void GPUBuffer::setSubData(uint64_t dst_byte_offset,
-                           const MaybeShared<DOMArrayBufferView>& src,
+                           const FlexibleArrayBufferView& src,
                            uint64_t src_byte_offset,
                            uint64_t byte_length,
                            ExceptionState& exception_state) {
   const uint8_t* src_base =
-      reinterpret_cast<const uint8_t*>(src.View()->BaseAddress());
-  size_t src_byte_length = src.View()->byteLength();
+      reinterpret_cast<const uint8_t*>(src.BaseAddressMaybeOnStack());
+  size_t src_byte_length = src.ByteLength();
 
   if (src_byte_offset > src_byte_length) {
     exception_state.ThrowRangeError("srcOffset is too large");

third_party/blink/renderer/modules/webgpu/gpu_buffer.h

@@ -7,6 +7,7 @@
 
 #include "third_party/blink/renderer/bindings/core/v8/script_promise.h"
 #include "third_party/blink/renderer/core/typed_arrays/array_buffer_view_helpers.h"
+#include "third_party/blink/renderer/core/typed_arrays/flexible_array_buffer_view.h"
 #include "third_party/blink/renderer/modules/webgpu/dawn_object.h"
 #include "third_party/blink/renderer/platform/bindings/exception_state.h"
 
@@ -33,7 +34,7 @@ class GPUBuffer : public DawnObject<WGPUBuffer> {
 
   // gpu_buffer.idl
   void setSubData(uint64_t dst_byte_offset,
-                  const MaybeShared<DOMArrayBufferView>& src,
+                  const FlexibleArrayBufferView& src,
                   uint64_t src_byte_offset,
                   uint64_t byte_length,
                   ExceptionState& exception_state);

third_party/blink/renderer/modules/webgpu/gpu_buffer.idl

@@ -9,7 +9,7 @@
 ] interface GPUBuffer {
     [RaisesException] void setSubData(
         unsigned long long dstOffset,
-        [AllowShared] ArrayBufferView src,
+        [AllowShared, FlexibleArrayBufferView] ArrayBufferView src,
         optional unsigned long long srcOffset = 0,
         optional unsigned long long byteLength = 0);
     [CallWith=ScriptState, RaisesException] Promise<ArrayBuffer> mapReadAsync();