exo: Set ExoSurface name before initializing window.
exo: Set ExoSurface name before initializing window.

This makes it possible to detect these windows when
aura::EnvObserver::OnWindowInitialized is called.

BUG=549781
TEST=exo_unittest --gtest_filter=SurfaceTest.*
TBR=denniskempin@chromium.org

Review URL: https://codereview.chromium.org/1497843004

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#363093}

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