Add precompiled headers to GN build for large targets.

chrome/test/BUILD.gn

Index: chrome/test/BUILD.gn
diff --git a/chrome/test/BUILD.gn b/chrome/test/BUILD.gn
index 563af1baf5382f269ffdee6ab61de2cd5dd5d7af..c496e3b05d20254c01fa219f1b3bad57d1ca87d3 100644
--- a/chrome/test/BUILD.gn
+++ b/chrome/test/BUILD.gn
@@ -84,6 +84,8 @@ source_set("test_support") {
     "logging/win/test_log_collector.h",
   ]
 
+  configs += [ "//build/config:precompiled_headers" ]
+
   # New deps should go in the non-iOS section below.
   public_deps = [
     "//content/test:test_support",
@@ -228,6 +230,7 @@ if (!is_android) {
                     ".",
                     "//chrome")
 
+    configs += [ "//build/config:precompiled_headers" ]
     defines = [ "HAS_OUT_OF_PROC_TEST_RUNNER" ]
     ldflags = []
 
@@ -547,6 +550,8 @@ if (!is_android) {
             ".",
             "//chrome")
 
+    configs += [ "//build/config:precompiled_headers" ]
+
     deps = [
       ":browser_tests_js_webui",
       ":sync_integration_test_support",
@@ -1153,6 +1158,7 @@ if (!is_android) {
                     ".",
                     "//chrome")
 
+    configs += [ "//build/config:precompiled_headers" ]
     defines = []
 
     deps = [