Add fuzzer for FDE CSS syntax parser.

testing/libfuzzer/BUILD.gn

Index: testing/libfuzzer/BUILD.gn
diff --git a/testing/libfuzzer/BUILD.gn b/testing/libfuzzer/BUILD.gn
index 5382313e0163e23d8d143f3b749ccf8e3c1c7fe6..3659c362257f2f86f01d834b43720d8058abc4a0 100644
--- a/testing/libfuzzer/BUILD.gn
+++ b/testing/libfuzzer/BUILD.gn
@@ -5,6 +5,8 @@
 import("../../pdfium.gni")
 
 config("libfuzzer_config") {
+  configs = [ "//third_party/pdfium:pdfium_core_config" ]
+
   defines = [
     "PNG_PREFIX",
     "PNG_USE_READ_MACROS",
@@ -122,6 +124,20 @@ if (pdf_enable_xfa) {
       ":libfuzzer_config",
     ]
   }
+  source_set("pdf_css_fuzzer") {
+    testonly = true
+    sources = [
+      "pdf_css_fuzzer.cc",
+    ]
+    deps = [
+      "//third_party/pdfium:pdfium",
+    ]
+    configs -= [ "//build/config/compiler:chromium_code" ]
+    configs += [
+      "//build/config/compiler:no_chromium_code",
+      ":libfuzzer_config",
+    ]
+  }
 }
 
 source_set("pdf_jpx_fuzzer") {