Fix a potential segfault in GpuVideoDecoder
Fix a potential segfault in GpuVideoDecoder

It's possible that NotifyError() is called between Initialize() and
CompleteInitialization() which would previously result in a null pointer
dereference. Now initialization is completed with an error.

BUG=623740

Review-Url: https://codereview.chromium.org/2109343002
Cr-Commit-Position: refs/heads/master@{#403251}
(cherry picked from commit 3154c1f3d402698d8914e95348bca3d4062f3541)

Review URL: https://codereview.chromium.org/2119663002 .

Cr-Commit-Position: 03d981dee550804c6934fd1a1d9cfa3c172affd3@{#554}
Cr-Branched-From: e9621a186760eb36d74098d9e33e4dd91c427b34@{#394939}

axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk