Consolidate test support code.

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("../pdfium.gni")
 
 group("samples") {
+  testonly = true
   deps = [
     ":pdfium_test",
     ":pdfium_diff",
   ]
 }
 
 config("pdfium_samples_config") {
   defines = [
     "PNG_PREFIX",
     "PNGPREFIX_H",
     "PNG_USE_READ_MACROS",
   ]
   if (pdf_enable_v8) {
     defines += [
       "PDF_ENABLE_V8",
     ]
   }
 }
 
 executable("pdfium_test") {
+  testonly = true
   sources = [
     "image_diff_png.cc",
     "pdfium_test.cc",
   ]
   deps = [
-    "//third_party/pdfium",
+    "//third_party/pdfium:pdfium",
+    "//third_party/pdfium:test_support",
     # Regardless of whether the library ships against system freetype,
     # always link this binary against the bundled one for consistency
     # of results across platforms.
     "//third_party/pdfium/third_party:fx_freetype",
     ":fx_lpng",
   ]
   if (pdf_enable_v8) {
     deps += [
       "//v8:v8_libplatform",
     ]
     include_dirs = [
       "//v8",
       "//v8/include",
     ]
   }
   configs += [ ":pdfium_samples_config" ]
 }
 
 executable("pdfium_diff") {
+  testonly = true
   sources = [
     "image_diff.cc",
     "image_diff_png.cc",
     "image_diff_png.h",
   ]
   deps = [
     "//third_party/pdfium",
     ":fx_lpng",
   ]
   configs -= [ "//build/config/compiler:chromium_code" ]
   configs += [
     ":pdfium_samples_config",
     "//build/config/compiler:no_chromium_code",
   ]
 }
 
 static_library("fx_lpng") {
+  testonly = true
   sources = [
     "fx_lpng/include/fx_png.h",
     "fx_lpng/src/fx_png.c",
     "fx_lpng/src/fx_pngerror.c",
     "fx_lpng/src/fx_pngget.c",
     "fx_lpng/src/fx_pngmem.c",
     "fx_lpng/src/fx_pngpread.c",
     "fx_lpng/src/fx_pngread.c",
     "fx_lpng/src/fx_pngrio.c",
     "fx_lpng/src/fx_pngrtran.c",
     "fx_lpng/src/fx_pngrutil.c",
     "fx_lpng/src/fx_pngset.c",
     "fx_lpng/src/fx_pngtrans.c",
     "fx_lpng/src/fx_pngwio.c",
     "fx_lpng/src/fx_pngwrite.c",
     "fx_lpng/src/fx_pngwtran.c",
     "fx_lpng/src/fx_pngwutil.c",
   ]
   include_dirs = [
     "../core/src/fxcodec/fx_zlib/include/",
   ]
   configs += [ ":pdfium_samples_config" ]
 }