Explicitly disable PlatformScreenshotTest.testScreenshot on Linux
Explicitly disable PlatformScreenshotTest.testScreenshot on Linux

BUG=563656
TBR=eakuefner@chromium.org

Review URL: https://codereview.chromium.org/1487043002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#362770}

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