Improve LayoutMultiColumnFlowThread::IsPageLogicalHeightKnown().

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

Index: third_party/WebKit/Source/core/layout/LayoutMultiColumnFlowThread.cpp
diff --git a/third_party/WebKit/Source/core/layout/LayoutMultiColumnFlowThread.cpp b/third_party/WebKit/Source/core/layout/LayoutMultiColumnFlowThread.cpp
index 7d2e99ab0ff5b13b2dbe3e9e09aa8b7a078d3ccf..be1c667ecd4b7f118de60f1313eccc175fc36256 100644
--- a/third_party/WebKit/Source/core/layout/LayoutMultiColumnFlowThread.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutMultiColumnFlowThread.cpp
@@ -363,9 +363,7 @@ bool LayoutMultiColumnFlowThread::NeedsNewWidth() const {
 }
 
 bool LayoutMultiColumnFlowThread::IsPageLogicalHeightKnown() const {
-  if (LayoutMultiColumnSet* column_set = LastMultiColumnSet())
-    return column_set->IsPageLogicalHeightKnown();
-  return false;
+  return all_columns_have_known_height_;
 }
 
 bool LayoutMultiColumnFlowThread::MayHaveNonUniformPageLogicalHeight() const {
@@ -543,6 +541,10 @@ void LayoutMultiColumnFlowThread::LayoutColumns(
     }
   }
 
+  // We'll start by assuming that all columns have some known height, and flip
+  // it to false if we discover that this isn't the case.
+  all_columns_have_known_height_ = true;
+
   for (LayoutBox* column_box = FirstMultiColumnBox(); column_box;
        column_box = column_box->NextSiblingMultiColumnBox()) {
     if (!column_box->IsLayoutMultiColumnSet()) {
@@ -557,6 +559,13 @@ void LayoutMultiColumnFlowThread::LayoutColumns(
       // because contents typically have changed.
       column_set->ResetColumnHeight();
     }
+    if (all_columns_have_known_height_ &&
+        !column_set->IsPageLogicalHeightKnown()) {
+      // If any of the column sets requires a layout pass before it has any
+      // clue about its height, we cannot fragment in this pass, just measure
+      // the block sizes.
+      all_columns_have_known_height_ = false;
+    }
     // Since column sets are regular block flow objects, and their position is
     // changed in regular block layout code (with no means for the multicol code
     // to notice unless we add hooks there), store the previous position now. If
@@ -945,6 +954,18 @@ void LayoutMultiColumnFlowThread::SkipColumnSpanner(
   }
 }
 
+bool LayoutMultiColumnFlowThread::FinishLayout() {
+  all_columns_have_known_height_ = true;
+  for (const auto* column_set = FirstMultiColumnSet(); column_set;
+       column_set = column_set->NextSiblingMultiColumnSet()) {
+    if (!column_set->IsPageLogicalHeightKnown()) {
+      all_columns_have_known_height_ = false;
+      break;
+    }
+  }
+  return !ColumnHeightsChanged();
+}
+
 // When processing layout objects to remove or when processing layout objects
 // that have just been inserted, certain types of objects should be skipped.
 static bool ShouldSkipInsertedOrRemovedChild(