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

chrome/browser/download/download_prefs.cc

Index: chrome/browser/download/download_prefs.cc
diff --git a/chrome/browser/download/download_prefs.cc b/chrome/browser/download/download_prefs.cc
index 05039fe5c5eb181f30070fdf77d3618f4df86067..bfe2f265799229dc5a62f35a9fa71f4cec092b12 100644
--- a/chrome/browser/download/download_prefs.cc
+++ b/chrome/browser/download/download_prefs.cc
@@ -138,7 +138,9 @@ DownloadPrefs::DownloadPrefs(Profile* profile) : profile_(profile) {
 
 #if defined(OS_WIN) || defined(OS_LINUX) || defined(OS_MACOSX)
   should_open_pdf_in_system_reader_ =
-      prefs->GetBoolean(prefs::kOpenPdfDownloadInSystemReader);
+      prefs->GetBoolean(prefs::kOpenPdfDownloadInSystemReader) ||
+      prefs->GetBoolean(prefs::kAlwaysOpenPdfExternally);
+  override_adobe_version_check_for_tests_ = false;
 #endif
 
   // If the download path is dangerous we forcefully reset it. But if we do
@@ -340,22 +342,26 @@ void DownloadPrefs::DisableAutoOpenBasedOnExtension(
 
 #if defined(OS_WIN) || defined(OS_LINUX) || defined(OS_MACOSX)
 void DownloadPrefs::SetShouldOpenPdfInSystemReader(bool should_open) {
-  if (should_open_pdf_in_system_reader_ == should_open)
-    return;
-  should_open_pdf_in_system_reader_ = should_open;
+  should_open_pdf_in_system_reader_ = should_open ||
+     profile_->GetPrefs()->GetBoolean(prefs::kAlwaysOpenPdfExternally);
   profile_->GetPrefs()->SetBoolean(prefs::kOpenPdfDownloadInSystemReader,
                                    should_open);
 }
 
 bool DownloadPrefs::ShouldOpenPdfInSystemReader() const {
 #if defined(OS_WIN)
-  if (IsAdobeReaderDefaultPDFViewer() &&
+  if (!override_adobe_version_check_for_tests_ &&

[asanka, 2016/09/28 17:27:53]

What should be the non-test behavior if |always_open_pdfs_externally| is set to
true and the Adobe reader is not up-to-date?

[pastarmovj, 2016/09/29 08:40:44]

It will cause a regular file download and let the user open it manually when
finished. This only prevents Chrome from automatically running Adobe Acrobat
Reader upon download completion.

P.S. The windows try bots actually trip over this check so they might be at risk
;)

+      IsAdobeReaderDefaultPDFViewer() &&
       !DownloadTargetDeterminer::IsAdobeReaderUpToDate()) {
       return false;
   }
 #endif
   return should_open_pdf_in_system_reader_;
 }
+
+void DownloadPrefs::OverrideAdobeVersionCheckForTests() {
+  override_adobe_version_check_for_tests_ = true;
+}
 #endif
 
 void DownloadPrefs::ResetAutoOpen() {