Remove unnecessary WebBlob constructors
Remove unnecessary WebBlob constructors

This is just a follow-up fix to apply sof's comments in
https://codereview.chromium.org/588073003/diff/160001/Source/web/WebBlob.cpp#oldcode45

BUG=340522
TBR=tkent

Review URL: https://codereview.chromium.org/618743005

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@183037 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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