Make ShowLineTreeForThis work on RootInlineBox and children-inline LayoutBlockFlow

When calling ShowLineTreeForThis() on RootInlineBox and children-
inline LayoutBlockFlow, the existing code searches for inline
structures in a wrong LayoutBlock, which is the block container of
the inline formatting context instead of the inline formatting
context itself.

This patch fixes the issue.

Bug: 821289
Change-Id: Icba7ee2b036649df5caba75050b4267188a8dbda
Reviewed-on: https://chromium-review.googlesource.com/961797Reviewed-by: Koji Ishii <kojii@chromium.org>
Commit-Queue: Xiaocheng Hu <xiaochengh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#543022}

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

@@ -1020,6 +1020,12 @@ LayoutBlock* LayoutObject::ContainingBlockForFixedPosition(
   return FindContainingBlock(container, skip_info);
 }
 
+const LayoutBlock* LayoutObject::InclusiveContainingBlock() const {
+  if (IsLayoutBlock())
+    return ToLayoutBlock(this);
+  return ContainingBlock();
+}
+
 LayoutBlock* LayoutObject::ContainingBlock(AncestorSkipInfo* skip_info) const {
   LayoutObject* object = Parent();
   if (!object && IsLayoutScrollbarPart())
@@ -1622,7 +1628,7 @@ void LayoutObject::ShowLayoutTreeForThis() const {
 }
 
 void LayoutObject::ShowLineTreeForThis() const {
-  if (LayoutBlock* cb = ContainingBlock()) {
+  if (const LayoutBlock* cb = InclusiveContainingBlock()) {
     if (cb->IsLayoutBlockFlow())
       ToLayoutBlockFlow(cb)->ShowLineTreeAndMark(nullptr, nullptr, nullptr,
                                                  nullptr, this);

third_party/WebKit/Source/core/layout/LayoutObject.h

@@ -1229,6 +1229,8 @@ class CORE_EXPORT LayoutObject : public ImageResourceObserver,
   // See LayoutBlock.h for some extra explanations on containing blocks.
   LayoutBlock* ContainingBlock(AncestorSkipInfo* = nullptr) const;
 
+  const LayoutBlock* InclusiveContainingBlock() const;
+
   bool CanContainAbsolutePositionObjects() const {
     return style_->CanContainAbsolutePositionObjects() ||
            CanContainFixedPositionObjects();

third_party/WebKit/Source/core/layout/line/InlineBox.cpp

@@ -21,6 +21,7 @@
 
 #include "core/layout/HitTestLocation.h"
 #include "core/layout/LayoutBlockFlow.h"
+#include "core/layout/api/LineLayoutAPIShim.h"
 #include "core/layout/api/LineLayoutBlockFlow.h"
 #include "core/layout/line/InlineFlowBox.h"
 #include "core/layout/line/RootInlineBox.h"
@@ -110,7 +111,13 @@ void InlineBox::ShowTreeForThis() const {
 }
 
 void InlineBox::ShowLineTreeForThis() const {
-  GetLineLayoutItem().ContainingBlock().ShowLineTreeAndMark(this, "*");
+  const LayoutBlock* containing_block =
+      LineLayoutAPIShim::LayoutObjectFrom(GetLineLayoutItem())
+          ->InclusiveContainingBlock();
+  if (containing_block) {
+    LineLayoutBox(const_cast<LayoutBlock*>(containing_block))
+        .ShowLineTreeAndMark(this, "*");
+  }
 }
 
 void InlineBox::DumpLineTreeAndMark(StringBuilder& string_builder,