[css-grid] Preemptively store intrinsic sizes during layout

third_party/WebKit/Source/core/layout/LayoutGrid.cpp

 /*
  * Copyright (C) 2011 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 262 matching lines @@
 
     // 1- First, the track sizing algorithm is used to resolve the sizes of the
     // grid columns.
     // At this point the logical width is always definite as the above call to
     // updateLogicalWidth() properly resolves intrinsic sizes. We cannot do the
     // same for heights though because many code paths inside
     // updateLogicalHeight() require a previous call to setLogicalHeight() to
     // resolve heights properly (like for positioned items for example).
     ComputeTrackSizesForDefiniteSize(kForColumns, available_space_for_columns);
 
+    // We take the chance to store the intrinsic sizes as the track sizing
+    // algorithm always compute them as part of its execution. Apart from saving

[jfernandez, 2017/04/21 14:48:02]

What do you mean with this sentence ?

[svillar, 2017/04/21 14:51:24]

In order to compute the intrinsic sizes we have to call the track sizing
algorithm. The algorithm always computes the intrinsic sizes because it's just
an intermediate result of its execution, is not avoidable and it does not
require any extra work.

+    // an algorithm execution, it fixes the use case of computing the preferred

[jfernandez, 2017/04/21 14:48:02]

Why we save an algorithm execution with this change ?

[svillar, 2017/04/21 14:51:23]

Because we wouldn't have to call the algorithm later if
minPreferredLogicalWidth() is called because they'd be already computed. I can
rephrase it if you want.

+    // logical widths *after* the layout process. Although not very common, this
+    // happens in the Mac (content::RenderViewImpl::didUpdateLayout()) or under
+    // some circumstances when grids are also flex items (crbug.com/708159).
+    if (PreferredLogicalWidthsDirty()) {
+      LayoutUnit scrollbar_width = LayoutUnit(ScrollbarLogicalWidth());
+      min_preferred_logical_width_ =
+          track_sizing_algorithm_.MinContentSize() + scrollbar_width;
+      max_preferred_logical_width_ =
+          track_sizing_algorithm_.MaxContentSize() + scrollbar_width;
+      ClearPreferredLogicalWidthsDirty();
+    }
+
     // 2- Next, the track sizing algorithm resolves the sizes of the grid rows,
     // using the grid column sizes calculated in the previous step.
     if (CachedHasDefiniteLogicalHeight()) {
       ComputeTrackSizesForDefiniteSize(
           kForRows, AvailableLogicalHeight(kExcludeMarginBorderPadding));
     } else {
       ComputeTrackSizesForIndefiniteSize(track_sizing_algorithm_, kForRows,
                                          grid_, min_content_height_,
                                          max_content_height_);
     }
@@ skipping 2096 matching lines @@
   if (direction == kForRows)
     return grid.NumTracks(kForRows);
 
   return grid.NumTracks(kForRows)
              ? grid.NumTracks(kForColumns)
              : GridPositionsResolver::ExplicitGridColumnCount(
                    StyleRef(), grid.AutoRepeatTracks(kForColumns));
 }
 
 }  // namespace blink