Change webpages_playback to run without requiring Google Storage access.
Change webpages_playback to run without requiring Google Storage access.

The motivation for this change is to make it easy for external contributors to generate SKPs from our page sets to use in their testing.

BUG=skia:2267
R=borenet@google.com

Review URL: https://codereview.chromium.org/298763002

google/skia-buildbot,google/skia-buildbot,Tiger66639/skia-buildbot,google/skia-buildbot,Tiger66639/skia-buildbot,google/skia-buildbot,Tiger66639/skia-buildbot,google/skia-buildbot,Tiger66639/skia-buildbot,Tiger66639/skia-buildbot,Tiger66639/skia-buildbot,google/skia-buildbot,google/skia-buildbot,Tiger66639/skia-buildbot,google/skia-buildbot