[Clipboard APIs] Handle null values for blobs OnRead()
Don't create |V8UnionBlobOrString| if the blob is null so that the null
value is handled in |ClipboardPromise::ResolveRead()| and it doesn't
perform an invalid conversion |ToResolvedPromise|.
Updated |ClipboardItemWithDOMStringSupport| flag status to experimental
Bug: 377251898
Change-Id: I47400f8a7671e4bb7b98b44d864b24b510e64835
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5993934
Reviewed-by: Christine Hollingsworth christinesm@chromium.org
Reviewed-by: Nate Chapin japhet@chromium.org
Reviewed-by: Ayu Ishii ayui@chromium.org
Commit-Queue: Sambamurthy Bandaru sambamurthy.bandaru@microsoft.com
Cr-Commit-Position: refs/heads/main@{#1379178}