media-libs/arc-mesa: Uprev to 12.1.0-pre2

This uprevs the upstream Mesa base to 12.1.0-devel based on the
following upstream git commit:

b010fa8 glsl: make sure UBO arrays are sized in ES

which matches current media-libs/mesa.

BUG=b:29036398
TEST=No significant regressions in dEQP inside the container

Change-Id: I2cd956a8db5c3da0d5cdff041494221ff8e52a4d
Reviewed-on: https://chromium-review.googlesource.com/368523
Commit-Ready: Tomasz Figa <tfiga@chromium.org>
Tested-by: Tomasz Figa <tfiga@chromium.org>
Reviewed-by: Nicolas Boichat <drinkcat@chromium.org>
(cherry picked from commit a684256d0695dd952670406f4683b28a6f7de446)
Reviewed-on: https://chromium-review.googlesource.com/369170
Reviewed-by: Tomasz Figa <tfiga@chromium.org>
Commit-Queue: Tomasz Figa <tfiga@chromium.org>
diff --git a/full.xml b/full.xml
index 1744e12..615397f 100644
--- a/full.xml
+++ b/full.xml
@@ -87,7 +87,7 @@
   <project name="chromiumos/platform/xorg-conf" path="src/platform/xorg-conf" />
   <project name="chromiumos/third_party/adhd" path="src/third_party/adhd" />
   <project name="chromiumos/third_party/android_mtdutils" path="src/third_party/android_mtdutils" />
-  <project name="chromiumos/third_party/mesa" path="src/third_party/arc-mesa" revision="refs/heads/release-R53-8530.B-arc-11.3.0-pre1" />
+  <project name="chromiumos/third_party/mesa" path="src/third_party/arc-mesa" revision="refs/heads/release-R53-8530.B-arc-12.1.0-pre2" />
   <project name="chromiumos/third_party/arm-trusted-firmware" path="src/third_party/arm-trusted-firmware">
     <annotation name="branch-mode" value="create" />
   </project>