[libfuzzer] switching libfuzzer to trace-pc-guard instrumentation.

build/config/sanitizers/sanitizers.gni

 # 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.
 
 import("//build/config/chrome_build.gni")
 import("//build/toolchain/toolchain.gni")
 
 declare_args() {
   # Compile for Address Sanitizer to find memory bugs.
   is_asan = false
@@ skipping 122 matching lines @@
   # Enable -fsanitize-coverage.
   use_sanitizer_coverage =
       use_libfuzzer || use_afl || sanitizer_coverage_flags != ""
 
   # Detect overflow/underflow for global objects.
   #
   # Mac: http://crbug.com/352073
   asan_globals = !is_mac
 }
 
-if (use_afl && sanitizer_coverage_flags == "") {
+if ((use_afl || use_libfuzzer) && sanitizer_coverage_flags == "") {
   sanitizer_coverage_flags = "trace-pc-guard"
 } else if (use_sanitizer_coverage && sanitizer_coverage_flags == "") {
   sanitizer_coverage_flags = "edge,indirect-calls,8bit-counters"
 }
 
 using_sanitizer =
     is_asan || is_lsan || is_tsan || is_msan || is_ubsan || is_ubsan_null ||
     is_ubsan_vptr || is_ubsan_security || use_sanitizer_coverage
 
 assert(!using_sanitizer || is_clang,
@@ skipping 29 matching lines @@
 assert(!is_debug || !(is_msan || is_ubsan || is_ubsan_null || is_ubsan_vptr),
        "Sanitizers should generally be used in release (set is_debug=false).")
 
 assert(!is_msan || (is_linux && current_cpu == "x64"),
        "MSan currently only works on 64-bit Linux and ChromeOS builds.")
 
 # ASAN build on Windows is not working in debug mode. Intercepting memory
 # allocation functions is hard on Windows and not yet implemented in LLVM.
 assert(!is_win || !is_debug || !is_asan,
        "ASan on Windows doesn't work in debug (set is_debug=false).")