Temporary return type inference for Skia change.
Temporary return type inference for Skia change.

The proposed Skia change can be seen at
https://codereview.chromium.org/869763002/ .
The return types need to be kept in sync, and this allows that.
This change will be undone after the Skia change lands,
effectively simply replacing the existing SkStream* return type
with SkStreamAsset*.

Review URL: https://codereview.chromium.org/871093003

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@188989 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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