Revert of exo: Disable RGBX fullscreen overlays. (patchset #1 id:1 of...

Revert of exo: Disable RGBX fullscreen overlays. (patchset #1 id:1 of https://codereview.chromium.org/2278803003/ )

Reason for revert:
crrev.com/2281033003 makes it so the compositor sends only one plane to Ozone.

In this way Ozone will accept an RGBX fullscreen plane.

Original issue's description:
> exo: Disable RGBX fullscreen overlays.
>
> Fullscreen overlays have been enabled on minnie.
> Unfortunately there are some issues in HardwareDisplayPlaneManager::
> AssignOverlayPlanes with RGBX buffers.
>
> This patch disables the overlay optimization for those buffers
> while we work on a fix.
>
> BUG=b/29430506
>
> Committed: https://crrev.com/18d1778af83ec9877cdf33401eddf4b082f766ef
> Cr-Commit-Position: refs/heads/master@{#414281}

TBR=reveman@chromium.org
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG=b/29430506

Review-Url: https://codereview.chromium.org/2287773002
Cr-Commit-Position: refs/heads/master@{#414853}

components/exo/display.cc

@@ -90,8 +90,8 @@ std::unique_ptr<Buffer> Display::CreateLinuxDMABufBuffer(
 
   // List of overlay formats that are known to be supported.
   // TODO(reveman): Determine this at runtime.
-  // TODO(dcastagna): Re-add RGBX_8888 format.
-  const gfx::BufferFormat kOverlayFormats[] = {gfx::BufferFormat::RGBA_8888};
+  const gfx::BufferFormat kOverlayFormats[] = {gfx::BufferFormat::RGBA_8888,
+                                               gfx::BufferFormat::RGBX_8888};
   bool is_overlay_candidate =
       std::find(std::begin(kOverlayFormats), std::end(kOverlayFormats),
                 format) != std::end(kOverlayFormats);