Use threadSafeBind() in BlobRegistry and remove BlobRegistryContext
Use threadSafeBind() in BlobRegistry and remove BlobRegistryContext

This CL replaces bind() used for cross-thread task posting with threadSafeBind().
BlobRegistryContext is removed and the arguments of the cross-thread tasks are directly passed to threadSafeBind().
No behavior changes because the deep copies created by BlobRegistryContext are now created in threadSafeBind().

BUG=479068, 478194

Review URL: https://codereview.chromium.org/1098803003

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@194255 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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