Fix context menu NullPointerException for getView

Widgets in ViewHolderItem of context menu sometimes cannot be retrieved
after inflation, this will causes NullPointerException when setting their
fields. Add null check for this case.

BUG=746482

Change-Id: If4ec3ee4e71a745a5dafcb651a027e1acd0f3849
Reviewed-on: https://chromium-review.googlesource.com/578745Reviewed-by: Ted Choc <tedchoc@chromium.org>
Commit-Queue: Lei Tian <ltian@google.com>
Cr-Commit-Position: refs/heads/master@{#488392}

chrome/android/java/src/org/chromium/chrome/browser/contextmenu/TabularContextMenuListAdapter.java

@@ -69,6 +69,9 @@ class TabularContextMenuListAdapter extends BaseAdapter {
             viewHolder = new ViewHolderItem();
             viewHolder.mIcon = (ImageView) convertView.findViewById(R.id.context_menu_icon);
             viewHolder.mText = (TextView) convertView.findViewById(R.id.context_text);
+            if (viewHolder.mText == null) {
+                throw new IllegalStateException("Context text not found in new view inflation");
+            }
             viewHolder.mShareIcon =
                     (ImageView) convertView.findViewById(R.id.context_menu_share_icon);
             viewHolder.mRightPadding =
@@ -77,6 +80,9 @@ class TabularContextMenuListAdapter extends BaseAdapter {
             convertView.setTag(viewHolder);
         } else {
             viewHolder = (ViewHolderItem) convertView.getTag();
+            if (viewHolder.mText == null) {
+                throw new IllegalStateException("Context text not found in view resuse");
+            }
         }
 
         viewHolder.mText.setText(menuItem.getTitle(mActivity));