Disable external navigation for file downloads.

chrome/android/java/src/org/chromium/chrome/browser/externalnav/ExternalNavigationDelegateImpl.java

Index: chrome/android/java/src/org/chromium/chrome/browser/externalnav/ExternalNavigationDelegateImpl.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/externalnav/ExternalNavigationDelegateImpl.java b/chrome/android/java/src/org/chromium/chrome/browser/externalnav/ExternalNavigationDelegateImpl.java
index 620fa92ad56e6b6bc637b9e8aa648c0764509cd1..f6946ecb7d8311c7477d287bd830b1ed745a7a3f 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/externalnav/ExternalNavigationDelegateImpl.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/externalnav/ExternalNavigationDelegateImpl.java
@@ -23,6 +23,7 @@ import android.provider.Telephony;
 import android.support.v7.app.AlertDialog;
 import android.text.TextUtils;
 import android.util.Log;
+import android.webkit.MimeTypeMap;
 
 import org.chromium.base.ApplicationState;
 import org.chromium.base.ApplicationStatus;
@@ -31,6 +32,7 @@ import org.chromium.base.PathUtils;
 import org.chromium.base.ThreadUtils;
 import org.chromium.chrome.R;
 import org.chromium.chrome.browser.ChromeActivity;
+import org.chromium.chrome.browser.ChromeFeatureList;
 import org.chromium.chrome.browser.ChromeTabbedActivity2;
 import org.chromium.chrome.browser.IntentHandler;
 import org.chromium.chrome.browser.document.ChromeLauncherActivity;
@@ -54,6 +56,7 @@ public class ExternalNavigationDelegateImpl implements ExternalNavigationDelegat
     private static final String PDF_VIEWER = "com.google.android.apps.docs";
     private static final String PDF_MIME = "application/pdf";
     private static final String PDF_SUFFIX = ".pdf";
+    private static final String PDF_EXTENSION = "pdf";
 
     protected final Context mApplicationContext;
     private final Tab mTab;
@@ -479,4 +482,14 @@ public class ExternalNavigationDelegateImpl implements ExternalNavigationDelegat
             ((ChromeActivity) context).getTabModelSelector().closeTab(tab);
         }
     }
+
+    @Override
+    public boolean isPdfDownload(String url) {
+        if (ChromeFeatureList.isEnabled(ChromeFeatureList.SYSTEM_DOWNLOAD_MANAGER)) return false;
+
+        String fileExtension = MimeTypeMap.getFileExtensionFromUrl(url);
+        if (TextUtils.isEmpty(fileExtension)) return false;
+
+        return PDF_EXTENSION.equals(fileExtension);
+    }
 }