Roll SwiftShader bf7a814..2b6ac18

https://swiftshader.googlesource.com/SwiftShader.git/+log/bf7a814..2b6ac18

BUG=

TBR=kbr@chromium.org

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;master.tryserver.chromium.android:android_optional_gpu_tests_rel

Review-Url: https://codereview.chromium.org/2906503002
Cr-Commit-Position: refs/heads/master@{#474465}

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': 'bf7a8145635e7dc6625596be127733ac7418cf21',
+  'swiftshader_revision': '2b6ac18d05ac8dd15577408ff9c531e96542958c',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling PDFium
   # and whatever else without interference from each other.