Fix an issue that referrer field is no longer exposed to pdfviewer

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 2591170e04f28eecbd5d0c05ae45bd93a72c7f83..3d4a98494ff1543d1504c1e097a57d54b03f8774 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
@@ -127,6 +127,10 @@ public class ExternalNavigationDelegateImpl implements ExternalNavigationDelegat
                             } else if (PDF_VIEWER.equals(pName)) {
                                 if (isPdfIntent(intent)) {
                                     intent.setClassName(pName, resolveInfo.activityInfo.name);
+                                    Uri referrer = new Uri.Builder().scheme(
+                                            IntentHandler.ANDROID_APP_REFERRER_SCHEME).authority(
+                                                    packageName).build();
+                                    intent.putExtra(Intent.EXTRA_REFERRER, referrer);
                                     hasPdfViewer = true;
                                     break;
                                 }