Enable precompiled headers for Blink on Windows.

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 30 matching lines @@
 config("core_include_dirs") {
   include_dirs = [
     "..",
     "$root_gen_dir/blink",
   ]
   if (is_android && use_openmax_dl_fft) {
     include_dirs += [ "//third_party/openmax_dl" ]
   }
 }
 
+import("//build/config/pch.gni")
+
+config("blink_core_pch") {
+  if (enable_precompiled_headers) {
+    if (is_win) {
+      # This is a string rather than a file GN knows about. It has to match
+      # exactly what's in the /FI flag below, and what might appear in the
+      # source code in quotes for an #include directive.
+      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",
     "//gin",
     "//skia",
     "//third_party/WebKit/Source/bindings/core/v8:bindings_core_v8_generated",
     "//third_party/WebKit/Source/core/inspector:generated",
     "//third_party/iccjpeg",
     "//third_party/libpng",
@@ skipping 133 matching lines @@
   if (is_mac) {
     libs = [
       "AppKit.framework",
       "Carbon.framework",
     ]
   }
 }
 
 source_set("testing") {
   configs += [
+    ":blink_core_pch",
+    "//third_party/WebKit/Source:config",
     "//third_party/WebKit/Source:inside_blink",
-    "//third_party/WebKit/Source:config",
   ]
 
   deps = [
     ":core",
     ":generated_testing_idls",
     "//third_party/WebKit/Source/bindings/core/v8:testing",
   ]
 
   sources = [
     "$blink_core_output_dir/testing/InternalSettingsGenerated.cpp",
@@ skipping 1093 matching lines @@
     "timing/PerformanceObserverTest.cpp",
     "timing/PerformanceTest.cpp",
     "workers/DedicatedWorkerTest.cpp",
     "workers/WorkerThreadTest.cpp",
     "workers/WorkerThreadTestHelper.h",
     "xml/XPathFunctionsTest.cpp",
     "xml/parser/SharedBufferReaderTest.cpp",
   ]
 
   configs += [
+    ":blink_core_pch",
     "//third_party/WebKit/Source:config",
     "//third_party/WebKit/Source:inside_blink",
   ]
 
   deps = [
     ":core",
     "//testing/gmock",
     "//testing/gtest",
   ]
 }
@@ skipping 29 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"
 }