[ash-md] Hides frame headers in overview mode not using a mask

There is a problem with clearing mask layers when the textures are reused.
Trying therefore to find a solution to hide the frame headers that does
not rely on masks.

BUG=624431

Review-Url: https://codereview.chromium.org/2129213003
Cr-Commit-Position: refs/heads/master@{#404573}
(cherry picked from commit c54b330fedbd77ed0d54532ec98418f7ce7ff6a6)

Review URL: https://codereview.chromium.org/2139873003 .

Cr-Commit-Position: refs/branch-heads/2785@{#95}
Cr-Branched-From: 68623971be0cfc492a2cb0427d7f478e7b214c24-refs/heads/master@{#403382}
4 files changed