This looks like a failure when we can't fit 4 columns onto the screen.  In the output do you see a warning like "WellGrid: trying to allocate for width..."?

I'm fairly shortly going to get a netbook with a similar resolution =)

No, nothing like that on the console. Note that I'm not running enough apps (AFAICT) to justify needing four columns?

Created attachment 143386 [details] [review]
[AppWell] Fall back to fewer than 4 columns if space limited

First eliminate the variable WELL_ITEM_HSPACING since it was 0
and thus effectively was not used.

Add a new variable WELL_ITEM_MIN_HSPACING which is the minimum
space between grid items we allow.  When computing layout, allow
for a number of columns less than 4 by using the minimum item
size.

Created attachment 143859 [details] [review]
[AppWell] Fall back to fewer than 4 columns if space limited

This is Colin's patch, rebased to the latest on master.

The patch looks good. One place that needs to be changed:

+            while (nColumns <= WELL_DEFAULT_COLUMNS &&
+                   nColumns <= children.length &&
+                   usedWidth <= forWidth) {
+                usedWidth += itemMinWidth;
+                nColumns++;
+            }
+            let minSizedHorizSpacingTotal = forWidth - (nColumns * itemMinWidth);
+            let allowedMinHorizSpacingTotal = Math.max(nColumns - 1, 0) * WELL_ITEM_MIN_HSPACING;
+            if (allowedMinHorizSpacingTotal > minSizedHorizSpacingTotal)
+                nColumns--;
+        }

The while loop increments nColumns one extra time. However, the end result is fine because nColumns is just always adjusted in the code that follows the while loop.

I think the code below should produce the same result and is shorter. I added a comment to compensate :). I was initially unsure why WELL_ITEM_MIN_HSPACING is only used in that one place, so thought that could use an explanation.

while (nColumns < WELL_DEFAULT_COLUMNS &&
       nColumns < children.length &&
       usedWidth + itemMinWidth <= forWidth) {
    // By including WELL_ITEM_MIN_HSPACING in usedWidth, we are ensuring
    // that the number of columns we end up with will allow the spacing
    // between the columns to be at least that value.
    usedWidth += itemMinWidth + WELL_ITEM_MIN_HSPACING;
    nColumns++;
}

Created attachment 143860 [details] [review]
[AppWell] Fall back to fewer than 4 columns if space limited

A patch with the change that I proposed in the previous comment.

Comment on attachment 143860 [details] [review]
[AppWell] Fall back to fewer than 4 columns if space limited

Sure.