WebRTC: Temporarily make libfuzzer bot use HEAD Clang.

scripts/slave/recipes/webrtc/libfuzzer.py

 # Copyright 2015 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 from recipe_engine.types import freeze
 
 
 DEPS = [
   'archive',
   'depot_tools/bot_update',
@@ skipping 47 matching lines @@
   webrtc.apply_bot_config(BUILDERS, webrtc.RECIPE_CONFIGS)
 
   api.webrtc.checkout()
   api.chromium.runhooks()
 
   # checkout llvm
   api.step('checkout llvm',
            [api.path.sep.join(['tools', 'clang', 'scripts', 'update.py']),
             '--force-local-build',
             '--without-android'],
-           cwd=api.path['checkout'])
+           cwd=api.path['checkout'],
+           # TODO(kjellander): Remove when crbug.com/591008 is fixed.
+           env={'LLVM_FORCE_HEAD_REVISION': 'YES'})
 
   api.chromium.run_gn(use_goma=False)
 
   step_result = api.python('calculate targets',
           api.path['depot_tools'].join('gn.py'),
           ['--root=%s' % str(api.path['checkout']),
            'refs',
            str(api.chromium.output_dir),
            '--all',
            '--type=executable',
            '--as=output',
            '//webrtc/test/fuzzers:webrtc_fuzzer_main',
           ],
           stdout=api.raw_io.output())
 
   targets = step_result.stdout.split()
   api.step.active_result.presentation.logs['targets'] = targets
   api.chromium.compile(targets=targets)
 
 
 def GenTests(api):
   for test in api.chromium.gen_tests_for_builders(BUILDERS):
     yield (test +
            api.step_data('calculate targets',
                stdout=api.raw_io.output('target1 target2 target3'))
            )