Avoid indefinite column block-size in initial column balancing.

The block-size of the column fragment in the initial column balancing
pass isn't used for anything (at least currently), but setting it to
kIndefiniteSize is pretty bogus. Don't do that.

https://chromium-review.googlesource.com/c/chromium/src/+/2611570
is about to introduce DCHECKs for such situations.

Change-Id: Ib6c7342ecc2f29a9d4d29c64bbaee8e2bde1243f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2626431Reviewed-by: David Grogan <dgrogan@chromium.org>
Reviewed-by: Ian Kilpatrick <ikilpatrick@chromium.org>
Commit-Queue: Morten Stenshorne <mstensho@chromium.org>
Cr-Commit-Position: refs/heads/master@{#843210}

third_party/blink/renderer/core/layout/ng/ng_block_layout_algorithm.cc

@@ -2277,15 +2277,21 @@ bool NGBlockLayoutAlgorithm::FinalizeForFragmentation() {
   }
 
   if (container_builder_.IsFragmentainerBoxType()) {
-    // We're building fragmentainers. Just copy the block-size from the
-    // constraint space. Calculating the size the regular way would cause some
-    // problems with overflow. For one, we don't want to produce a break token
-    // if there's no child content that requires it.
+    // We're building fragmentainers. Unless we're in the initial column
+    // balancing pass (when fragmentainer block-size is unknown), just copy the
+    // block-size from the constraint space. Calculating the size the regular
+    // way would cause some problems with overflow. For one, we don't want to
+    // produce a break token if there's no child content that requires it. If we
+    // *are* in the initial column balancing pass, on the other hand, just skip
+    // this part, and keep the fragment size calculated by the block layout
+    // algorithm (rather than setting it to indefinite).
+    if (ConstraintSpace().HasKnownFragmentainerBlockSize()) {
       LayoutUnit consumed_block_size =
           BreakToken() ? BreakToken()->ConsumedBlockSize() : LayoutUnit();
       LayoutUnit block_size = ConstraintSpace().FragmentainerBlockSize();
       container_builder_.SetFragmentBlockSize(block_size);
       container_builder_.SetConsumedBlockSize(consumed_block_size + block_size);
+    }
     return true;
   }