[NTP] Propagate OfflineId from C++ for Downloads.

chrome/android/java/src/org/chromium/chrome/browser/ntp/NewTabPage.java

Index: chrome/android/java/src/org/chromium/chrome/browser/ntp/NewTabPage.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/ntp/NewTabPage.java b/chrome/android/java/src/org/chromium/chrome/browser/ntp/NewTabPage.java
index d5fda2a22ef9971294c97498d2bb45d4f01bca17..9842361011d29ae17efe41bc9f9c02a478dad8e4 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/ntp/NewTabPage.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/ntp/NewTabPage.java
@@ -349,7 +349,6 @@ public class NewTabPage
             mSnippetsBridge.onSuggestionOpened(article, windowOpenDisposition);
             NewTabPageUma.recordAction(NewTabPageUma.ACTION_OPENED_SNIPPET);
 
-            // TODO(vitaliii): Propagate OfflineId for offline page downloads from C++.
             if (article.isDownload() && article.mIsDownloadedAsset) {
                 DownloadUtils.openFile(
                         article.getDownloadAssetFile(), article.getDownloadAssetMimeType(), false);
@@ -394,8 +393,10 @@ public class NewTabPage
             int tabIndex = TabModelUtils.getTabIndexById(tabModel, tabId);
             if (tabIndex == TabModel.INVALID_TAB_INDEX) return false;
             TabModelUtils.setIndex(tabModel, tabIndex);
+            assert recentTabArticle.getOfflinePageOfflineId().equals(
+                    Long.parseLong(recentTabArticle.getRecentTabId()));

[Marc Treib, 2016/11/16 15:22:58]

If OfflinePageId and RecentTabId are always the same, can we get rid of
RecentTabId?

[vitaliii, 2016/11/16 15:45:08]

I am not sure whether this is guaranteed and whether this is not an
implementation detail. Last time I checked there were no comments when they
initialize one with another. Moreover, now I am confused how they ensure that
recent tab offline pages ids do not collide with others. Thus, since we already
passing it anyway, staying safe seems like a good choice :) 

[Marc Treib, 2016/11/16 15:55:56]

Aren't offline IDs unique?

Well, do we do anything with the recent tab ID anywhere? If not, then I still
vote we get rid of it.

[vitaliii, 2016/11/16 15:59:22]

They must be. That is my concern how they ensure this while having OfflineId =
TabId for recent tabs.
Yes, we find the tab by tab ID (a few lines above this comment).

             OfflinePageUtils.openInExistingTab(recentTabArticle.mUrl,
-                    Long.parseLong(recentTabArticle.getRecentTabId()), tabModel.getTabAt(tabIndex));
+                    recentTabArticle.getOfflinePageOfflineId(), tabModel.getTabAt(tabIndex));
             return true;
         }