Adds a pref and a policy to decide if PDFs should always be opened externally.

chrome/browser/download/download_prefs_unittest.cc

Index: chrome/browser/download/download_prefs_unittest.cc
diff --git a/chrome/browser/download/download_prefs_unittest.cc b/chrome/browser/download/download_prefs_unittest.cc
index 68406f6d03e5b0d18494be9f223c9bf740c9b1de..1e5dfe346350136fc6d74b56cd58362220181604 100644
--- a/chrome/browser/download/download_prefs_unittest.cc
+++ b/chrome/browser/download/download_prefs_unittest.cc
@@ -117,3 +117,18 @@ TEST(DownloadPrefsTest, AutoOpenCheckIsCaseInsensitive) {
   EXPECT_TRUE(prefs.IsAutoOpenEnabledBasedOnExtension(
       base::FilePath(FILE_PATH_LITERAL("x.Bar"))));
 }
+
+#if defined(OS_WIN) || defined(OS_LINUX) || defined(OS_MACOSX)
+TEST(DownloadPrefsTest, AlwaysOpenPdfExternally) {
+  content::TestBrowserThreadBundle threads_are_required_for_testing_profile;
+  TestingProfile profile;
+  profile.GetPrefs()->SetBoolean(prefs::kOpenPdfDownloadInSystemReader, false);
+  profile.GetPrefs()->SetBoolean(prefs::kPluginsAlwaysOpenPdfExternally, true);
+  DownloadPrefs prefs(&profile);
+  prefs.DisableAdobeVersionCheckForTests();
+
+  EXPECT_TRUE(prefs.ShouldOpenPdfInSystemReader());
+  EXPECT_TRUE(prefs.IsAutoOpenEnabledBasedOnExtension(
+      base::FilePath(FILE_PATH_LITERAL("doc.pdf"))));
+}
+#endif