Prioritize first-lines over orphans when deciding whether to propagate a strut.

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

Index: third_party/WebKit/Source/core/layout/LayoutBlockFlow.cpp
diff --git a/third_party/WebKit/Source/core/layout/LayoutBlockFlow.cpp b/third_party/WebKit/Source/core/layout/LayoutBlockFlow.cpp
index 8eb135ee1321d7e0af1339975e75480165e35f3a..41e68517f1d4ebfa8931d9935df53db3b1a21006 100644
--- a/third_party/WebKit/Source/core/layout/LayoutBlockFlow.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutBlockFlow.cpp
@@ -798,26 +798,37 @@ LayoutUnit LayoutBlockFlow::adjustBlockChildForPagination(LayoutUnit logicalTop,
 
 static bool shouldSetStrutOnBlock(const LayoutBlockFlow& block, const RootInlineBox& lineBox, LayoutUnit lineLogicalOffset, int lineIndex, LayoutUnit pageLogicalHeight)
 {
-    bool wantsStrutOnBlock = false;
-    if (!block.style()->hasAutoOrphans() && block.style()->orphans() >= lineIndex) {
-        // Not enough orphans here. Push the entire block to the next column / page as an
-        // attempt to better satisfy the orphans requirement.
-        wantsStrutOnBlock = true;
-    } else if (lineBox == block.firstRootBox() && lineLogicalOffset == block.borderAndPaddingBefore()) {
+    if (lineBox == block.firstRootBox()) {
         // This is the first line in the block. We can take the whole block with us to the next page
         // or column, rather than keeping a content-less portion of it in the previous one. Only do
         // this if the line is flush with the content edge of the block, though. If it isn't, it
         // means that the line was pushed downwards by preceding floats that didn't fit beside the
         // line, and we don't want to move all that, since it has already been established that it
-        // fits nicely where it is.
+        // fits nicely where it is. In this case we have a class "C" break point [1] in front of
+        // this line.
+        //
+        // [1] https://drafts.csswg.org/css-break/#possible-breaks
+        if (lineLogicalOffset > block.borderAndPaddingBefore())
+            return false;
+
         LayoutUnit lineHeight = lineBox.lineBottomWithLeading() - lineBox.lineTopWithLeading();
         LayoutUnit totalLogicalHeight = lineHeight + lineLogicalOffset.clampNegativeToZero();
         // It's rather pointless to break before the block if the current line isn't going to
         // fit in the same column or page, so check that as well.
-        if (totalLogicalHeight <= pageLogicalHeight)
-            wantsStrutOnBlock = true;
+        if (totalLogicalHeight > pageLogicalHeight)
+            return false;
+    } else {
+        if (block.style()->hasAutoOrphans() || lineIndex > block.style()->orphans())
+            return false;
+
+        // Not enough orphans here. Push the entire block to the next column / page as an attempt to
+        // better satisfy the orphans requirement.
+        //
+        // Note that we should ideally check if the first line in the block is flush with the
+        // content edge of the block here, because if it isn't, we should break at the class "C"
+        // break point in front of the first line, rather than before the entire block.
     }
-    return wantsStrutOnBlock && block.allowsPaginationStrut();
+    return block.allowsPaginationStrut();
 }
 
 void LayoutBlockFlow::adjustLinePositionForPagination(RootInlineBox& lineBox, LayoutUnit& delta)