Roll SwiftShader 83a6bb9..a781af7

https://swiftshader.googlesource.com/SwiftShader.git/+log/83a6bb9..a781af7

BUG=737875

TEST=bots

CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.win:win_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel,linux_chromium_cfi_rel_ng;master.tryserver.chromium.android:android_optional_gpu_tests_rel

Change-Id: Ib4a779492cd09ba17bd6dda86cb1b0ef9685a756
Reviewed-on: https://chromium-review.googlesource.com/564665Reviewed-by: Alexis Hétu <sugoi@chromium.org>
Commit-Queue: Nicolas Capens <nicolascapens@google.com>
Cr-Commit-Position: refs/heads/master@{#485286}

DEPS

@@ -60,7 +60,7 @@ vars = {
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling SwiftShader
   # and whatever else without interference from each other.
-  'swiftshader_revision': '83a6bb93fd825b975161546ff92d6fb77a7a9c22',
+  'swiftshader_revision': 'a781af7d5a1930d82d20c0cbc9d66fc8a42391e0',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling PDFium
   # and whatever else without interference from each other.