The Mac ASAN bot on the chromium.gpu.fyi waterfall has been red for a while. It's building again after the fixes in Issue 742004 and earlier bugs and is catching a real bug now in gles2_conform_test. Full excerpt from one of the failures follows. Investigating.

==3600==ERROR: AddressSanitizer: stack-buffer-overflow on address 0x7fff580d186d at pc 0x00010905a24e bp 0x7fff580ce7f0 sp 0x7fff580ce7e8
READ of size 1 at 0x7fff580d186d thread T0
    #0 0x10905a24d in gpu::gles2::Program::Update() ??:0:0
    #1 0x109067e56 in gpu::gles2::Program::Link(gpu::gles2::ShaderManager*, gpu::gles2::Program::VaryingsPackingOption, gpu::gles2::GLES2DecoderClient*) ??:0:0
    #2 0x108f56ae6 in gpu::gles2::GLES2DecoderImpl::DoLinkProgram(unsigned int) ??:0:0
    #3 0x108ed0bf8 in gpu::gles2::GLES2DecoderImpl::HandleLinkProgram(unsigned int, void const volatile*) ??:0:0
    #4 0x108f37928 in gpu::error::Error gpu::gles2::GLES2DecoderImpl::DoCommandsImpl<false>(unsigned int, void const volatile*, int, int*) ??:0:0
    #5 0x108e29a78 in gpu::CommandBufferService::Flush(int, gpu::AsyncAPIInterface*) ??:0:0
    #6 0x108e282a4 in gpu::CommandBufferDirect::Flush(int) ??:0:0
    #7 0x107d996db in gpu::CommandBufferHelper::Flush() ??:0:0
    #8 0x107d9a17e in gpu::CommandBufferHelper::Finish() ??:0:0
    #9 0x107f934dd in gpu::gles2::GLES2Implementation::WaitForCmd() ??:0:0
    #10 0x107feb267 in gpu::gles2::GLES2Implementation::IsShader(unsigned int) ??:0:0
    #11 0x107d780dc in GTFLinkProgram_2_0 ??:0:0
    #12 0x107d38430 in GTFTestBuildGLApply ??:0:0
    #13 0x107d552fb in GTFRunTest ??:0:0
    #14 0x107d50464 in GTFRunTestDriver ??:0:0
    #15 0x107d23d0f in GTFRun ??:0:0
    #16 0x107d189b3 in GTFInitEGL ??:0:0
    #17 0x107d22939 in GTFMain ??:0:0
    #18 0x107d8dfa8 in main ??:0:0
    #19 0x7fff9475d234 in start ??:0:0
Address 0x7fff580d186d is located in stack of thread T0 at offset 301 in frame
    #0 0x107d53fbf in GTFRunTest ??:0:0
  This frame has 9 object(s):
    [32, 40) 'mode'
    [64, 72) 'pattern'
    [96, 104) 'root'
    [128, 132) 'err_line'
    [144, 160) 'dir'
    [176, 192) 'name'
    [208, 224) 'ext'
    [240, 256) 'group_name'
    [272, 288) 'err_msg' <== Memory access at offset 301 overflows this variable
HINT: this may be a false positive if your program uses some custom stack unwind mechanism or swapcontext
      (longjmp and C++ exceptions *are* supported)
SUMMARY: AddressSanitizer: stack-buffer-overflow (/b/s/w/ir/out/Release/gles2_conform_test_windowless:x86_64+0x10152d24d)
Shadow bytes around the buggy address:
  0x1fffeb01a2b0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x1fffeb01a2c0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x1fffeb01a2d0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x1fffeb01a2e0: 00 00 00 00 00 00 00 00 f1 f1 f1 f1 00 f2 f2 f2
  0x1fffeb01a2f0: 00 f2 f2 f2 00 f2 f2 f2 04 f2 00 00 f2 f2 00 00
=>0x1fffeb01a300: f2 f2 00 00 f2 f2 00 00 f2 f2 00 00 f3[f3]f3 f3
  0x1fffeb01a310: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x1fffeb01a320: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x1fffeb01a330: 00 00 00 00 00 00 00 00 00 00 00 00 f1 f1 f1 f1
  0x1fffeb01a340: 00 00 f2 f2 00 00 f2 f2 00 00 f2 f2 00 00 f2 f2
  0x1fffeb01a350: 00 00 f2 f2 00 f2 f2 f2 04 f2 00 00 00 f3 f3 f3
Shadow byte legend (one shadow byte represents 8 application bytes):
  Addressable:           00
  Partially addressable: 01 02 03 04 05 06 07
  Heap left redzone:       fa
  Freed heap region:       fd
  Stack left redzone:      f1
  Stack mid redzone:       f2
  Stack right redzone:     f3
  Stack after return:      f5
  Stack use after scope:   f8
  Global redzone:          f9
  Global init order:       f6
  Poisoned by user:        f7
  Container overflow:      fc
  Array cookie:            ac
  Intra object redzone:    bb
  ASan internal:           fe
  Left alloca redzone:     ca
  Right alloca redzone:    cb
==3600==ABORTING
gen/gpu/gles2_conform_support/gles2_conform_test_autogen.cc:566: Failure
Value of: RunGLES2ConformTest("GL2Tests/validate_program/input.run")
  Actual: false
Expected: true
[  FAILED  ] GLES2ConformTest.GL2Tests_validate_program_input_run (262 ms)