Drop MSVC pch warning avoidance.

third_party/WebKit/Source/core/BUILD.gn

 # Copyright 2014 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/chromecast_build.gni")
 import("//build/toolchain/toolchain.gni")
 import("//build/config/ui.gni")
 import("//build/split_static_library.gni")
 import("//testing/libfuzzer/fuzzer_test.gni")
 import("//third_party/WebKit/Source/bindings/bindings.gni")
@@ skipping 48 matching lines @@
       precompiled_header = rebase_path("win/Precompile-core.h", root_build_dir)
 
       # This is a file that GN will compile with the above header. It will be
       # implicitly added to the sources (potentially multiple times, with one
       # variant for each language used in the target).
       precompiled_source =
           "//third_party/WebKit/Source/core/win/Precompile-core.cpp"
 
       # Force include the header.
       cflags = [ "/FI$precompiled_header" ]
-
-      # Disable warning for "this file was empty after preprocessing". This
-      # error is generated only in C mode for ANSI compatibility. It conflicts
-      # with precompiled headers since the source file that's "compiled" for
-      # making the precompiled header is empty.
-      #
-      # This error doesn't happen every time. In VS2013, it seems if the .pch
-      # file doesn't exist, no error will be generated (probably MS tested this
-      # case but forgot the other one?). To reproduce this error, do a build,
-      # then delete the precompile.c.obj file, then build again.
-      cflags_c = [ "/wd4206" ]
     }
   }
 }
 
 core_config_add += [ ":blink_core_pch" ]
 
 source_set("generated") {
   deps = [
     ":core_generated",
     ":prerequisites",
@@ skipping 1251 matching lines @@
   sources = [
     "frame/csp/ContentSecurityPolicyFuzzer.cpp",
   ]
   deps = [
     ":core",
     "//third_party/WebKit/Source/platform:blink_fuzzer_test_support",
   ]
   dict = "//testing/libfuzzer/fuzzers/dicts/content_security_policy.dict"
   seed_corpus = "//testing/libfuzzer/fuzzers/content_security_policy_corpus"
 }