Fixup coverage build

samples/BUILD.gn

 # Copyright 2014 PDFium 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/sanitizers/sanitizers.gni")
 import("../pdfium.gni")
 
 group("samples") {
   testonly = true
   deps = [
     ":pdfium_diff",
     ":pdfium_test",
   ]
 }
 
 config("pdfium_samples_config") {
+  cflags = []
+  ldflags = []
   defines = [
     "PNG_PREFIX",
     "PNG_USE_READ_MACROS",
   ]
   include_dirs = [ ".." ]
   if (pdf_enable_v8) {
     defines += [ "PDF_ENABLE_V8" ]
   }
   if (pdf_enable_xfa) {
     defines += [ "PDF_ENABLE_XFA" ]
   }
   if (pdf_use_skia) {
     defines += [ "PDF_ENABLE_SKIA" ]
   }
+  if (use_coverage && is_clang) {
+    cflags += [
+      "--coverage",
+      "-g",
+      "-O0",
+    ]
+    ldflags += [ "--coverage" ]
+  }
 }
 
 executable("pdfium_test") {
   testonly = true
   sources = [
     "image_diff_png.cc",
     "image_diff_png.h",
     "pdfium_test.cc",
   ]
   deps = [
@@ skipping 38 matching lines @@
   ]
   if (!pdf_enable_xfa) {
     deps += [ "../third_party:fx_lpng" ]
   }
   configs -= [ "//build/config/compiler:chromium_code" ]
   configs += [
     ":pdfium_samples_config",
     "//build/config/compiler:no_chromium_code",
   ]
 }