Eliminate RenderedPosition::UncachedInlineBox with Optional

RenderedPosition caches two |InlineBox*|, and uses 1 as the magic value
indicating the uncached value, which is a hacky approach. This patch
changes them to Optional<InlineBox*> to make the caching not hacky.

Bug: 771398
Change-Id: If8bef20755fcc75b04093de6c2211138d336600e
Reviewed-on: https://chromium-review.googlesource.com/702924
Commit-Queue: Xiaocheng Hu <xiaochengh@chromium.org>
Commit-Queue: Emil A Eklund <eae@chromium.org>
Reviewed-by: Emil A Eklund <eae@chromium.org>
Cr-Commit-Position: refs/heads/master@{#506861}

third_party/WebKit/Source/core/editing/RenderedPosition.cpp

@@ -78,11 +78,7 @@ RenderedPosition::RenderedPosition(const VisiblePositionInFlatTree& position)
 
 RenderedPosition::RenderedPosition(const Position& position,
                                    TextAffinity affinity)
-    : layout_object_(nullptr),
-      inline_box_(nullptr),
-      offset_(0),
-      prev_leaf_child_(UncachedInlineBox()),
-      next_leaf_child_(UncachedInlineBox()) {
+    : layout_object_(nullptr), inline_box_(nullptr), offset_(0) {
   if (position.IsNull())
     return;
   InlineBoxPosition box_position = ComputeInlineBoxPosition(position, affinity);
@@ -97,11 +93,7 @@ RenderedPosition::RenderedPosition(const Position& position,
 
 RenderedPosition::RenderedPosition(const PositionInFlatTree& position,
                                    TextAffinity affinity)
-    : layout_object_(nullptr),
-      inline_box_(nullptr),
-      offset_(0),
-      prev_leaf_child_(UncachedInlineBox()),
-      next_leaf_child_(UncachedInlineBox()) {
+    : layout_object_(nullptr), inline_box_(nullptr), offset_(0) {
   if (position.IsNull())
     return;
   InlineBoxPosition box_position = ComputeInlineBoxPosition(position, affinity);
@@ -115,15 +107,15 @@ RenderedPosition::RenderedPosition(const PositionInFlatTree& position,
 }
 
 InlineBox* RenderedPosition::PrevLeafChild() const {
-  if (prev_leaf_child_ == UncachedInlineBox())
+  if (!prev_leaf_child_.has_value())
     prev_leaf_child_ = inline_box_->PrevLeafChildIgnoringLineBreak();
-  return prev_leaf_child_;
+  return prev_leaf_child_.value();
 }
 
 InlineBox* RenderedPosition::NextLeafChild() const {
-  if (next_leaf_child_ == UncachedInlineBox())
+  if (!next_leaf_child_.has_value())
     next_leaf_child_ = inline_box_->NextLeafChildIgnoringLineBreak();
-  return next_leaf_child_;
+  return next_leaf_child_.value();
 }
 
 bool RenderedPosition::IsEquivalent(const RenderedPosition& other) const {

third_party/WebKit/Source/core/editing/RenderedPosition.h

@@ -35,6 +35,7 @@
 #include "core/editing/Forward.h"
 #include "core/layout/line/InlineBox.h"
 #include "platform/wtf/Allocator.h"
+#include "platform/wtf/Optional.h"
 
 namespace blink {
 
@@ -125,32 +126,19 @@ class CORE_EXPORT RenderedPosition {
   InlineBox* inline_box_;
   int offset_;
 
-  static InlineBox* UncachedInlineBox() {
-    return reinterpret_cast<InlineBox*>(1);
-  }
-  // Needs to be different form 0 so pick 1 because it's also on the null page.
-
-  mutable InlineBox* prev_leaf_child_;
-  mutable InlineBox* next_leaf_child_;
+  mutable Optional<InlineBox*> prev_leaf_child_;
+  mutable Optional<InlineBox*> next_leaf_child_;
 
   FRIEND_TEST_ALL_PREFIXES(RenderedPositionTest, GetSamplePointForVisibility);
 };
 
 inline RenderedPosition::RenderedPosition()
-    : layout_object_(nullptr),
-      inline_box_(nullptr),
-      offset_(0),
-      prev_leaf_child_(UncachedInlineBox()),
-      next_leaf_child_(UncachedInlineBox()) {}
+    : layout_object_(nullptr), inline_box_(nullptr), offset_(0) {}
 
 inline RenderedPosition::RenderedPosition(LayoutObject* layout_object,
                                           InlineBox* box,
                                           int offset)
-    : layout_object_(layout_object),
-      inline_box_(box),
-      offset_(offset),
-      prev_leaf_child_(UncachedInlineBox()),
-      next_leaf_child_(UncachedInlineBox()) {}
+    : layout_object_(layout_object), inline_box_(box), offset_(offset) {}
 
 CORE_EXPORT bool LayoutObjectContainsPosition(LayoutObject*, const Position&);