Make NGInlineItemsBuilder construct whitespace-collapsed offset mapping

third_party/WebKit/Source/core/layout/ng/inline/ng_offset_mapping_builder.cc

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "core/layout/ng/inline/ng_offset_mapping_builder.h"
+
+#include "platform/wtf/text/StringBuilder.h"
+
+namespace blink {
+
+NGOffsetMappingBuilder::NGOffsetMappingBuilder() {
+  mapping_.push_back(0);
+}
+
+void NGOffsetMappingBuilder::AppendIdentityMapping(unsigned length) {
+  DCHECK_GT(length, 0u);
+  DCHECK(!mapping_.IsEmpty());
+  for (unsigned i = 0; i < length; ++i) {
+    unsigned next = mapping_.back() + 1;
+    mapping_.push_back(next);
+  }
+}
+
+void NGOffsetMappingBuilder::AppendCollapsedMapping(unsigned length) {
+  DCHECK_GT(length, 0u);
+  DCHECK(!mapping_.IsEmpty());
+  const unsigned back = mapping_.back();
+  for (unsigned i = 0; i < length; ++i)
+    mapping_.push_back(back);
+}
+
+void NGOffsetMappingBuilder::CollapseTrailingSpace(unsigned skip_length) {
+  DCHECK(!mapping_.IsEmpty());
+
+  // Find the |skipped_count + 1|-st last uncollapsed character. By collapsing
+  // it, all mapping values beyond this position are decremented by 1.
+  unsigned skipped_count = 0;
+  for (unsigned i = mapping_.size() - 1; skipped_count <= skip_length; --i) {
+    DCHECK_GT(i, 0u);
+    if (mapping_[i] != mapping_[i - 1])
+      ++skipped_count;
+    --mapping_[i];
+  }
+}
+
+Vector<unsigned> NGOffsetMappingBuilder::DumpOffsetMappingForTesting() const {
+  return mapping_;
+}
+
+}  // namespace blink