atob() clones the output more than necessary

[Jarred Sumner]

From: https://github.com/WebKit/WebKit/blob/de456d04c10080ce71f48d14b3a9d278854d5f8a/Source/WebCore/page/Base64Utilities.cpp#L53


    auto decodedData = base64Decode(encodedString, Base64DecodeMode::DefaultValidatePaddingAndIgnoreWhitespace);
    if (!decodedData)
        return Exception { InvalidCharacterError };

    return String(decodedData->data(), decodedData->size());


String(const char*, unsigned) calls StringImpl::create(reinterpret_cast<const LChar*>(ptr), length).

This is an extra clone, from the Vector<uint8_t> -> StringImpl. Seems like moving the Vector would also clone it.

Possible suggestions:
- base64Decode could have a template arg to use WTF::StringBuilder?
- Maybe there's a way using ExternalStringImpl?

[Radar WebKit Bug Importer]

<rdar://problem/111993365>

[Keith Miller]

Pull request: https://github.com/WebKit/WebKit/pull/15781

[EWS]

Committed 266016@main (985e10033996): <https://commits.webkit.org/266016@main>

Reviewed commits have been landed. Closing PR #15781 and removing active labels.