[Idle time spell checker] Add paragraph-level heuristic to hot mode requester

third_party/WebKit/Source/core/editing/spellcheck/HotModeSpellCheckRequester.cpp

 // 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/editing/spellcheck/HotModeSpellCheckRequester.h"
 
 #include "core/editing/EditingUtilities.h"
 #include "core/editing/Editor.h"
 #include "core/editing/VisiblePosition.h"
 #include "core/editing/commands/CompositeEditCommand.h"
 #include "core/editing/commands/TypingCommand.h"
 #include "core/editing/iterators/BackwardsCharacterIterator.h"
 #include "core/editing/iterators/CharacterIterator.h"
 #include "core/editing/markers/DocumentMarkerController.h"
 #include "core/editing/spellcheck/SpellCheckRequester.h"
 #include "core/editing/spellcheck/SpellChecker.h"
 
 namespace blink {
 
 namespace {
 
+const int kHotModeCheckAllThreshold = 128;
 const int kHotModeChunkSize = 1024;
 
 EphemeralRange AdjacentWordIfExists(const Position& pos) {
   const VisiblePosition& visible_pos = CreateVisiblePosition(pos);
   const VisiblePosition& word_start = PreviousWordPosition(visible_pos);
   if (word_start.IsNull())
     return EphemeralRange();
   const VisiblePosition& word_end = EndOfWord(word_start);
   if (word_end.IsNull())
     return EphemeralRange();
@@ skipping 26 matching lines @@
     return false;
   if (editable.VisibleBoundsInVisualViewport().IsEmpty())
     return false;
   // TODO(xiaochengh): Design more aggressive strategies to reduce checking when
   // we are just moving selection around without modifying anything.
   return true;
 }
 
 EphemeralRange CalculateHotModeCheckingRange(const Element& editable,
                                              const Position& position) {
+  // Check everything in |editable| if its total length is short.
   const EphemeralRange& full_range = EphemeralRange::RangeOfContents(editable);
   const int full_length = TextIterator::RangeLength(full_range.StartPosition(),
                                                     full_range.EndPosition());
-  if (full_length <= kHotModeChunkSize)
+  // TODO(xiaochengh): There is no need to check if |full_length <= 2|, since
+  // we don't consider two characters as misspelled. However, a lot of layout
+  // tests depend on "zz" as misspelled, which should be changed.
+  if (full_length <= kHotModeCheckAllThreshold)
     return full_range;
 
+  // Otherwise, if |position| is in a short paragraph, check the paragraph.
+  const EphemeralRange& paragraph_range =
+      ExpandToParagraphBoundary(EphemeralRange(position));
+  const int paragraph_length = TextIterator::RangeLength(
+      paragraph_range.StartPosition(), paragraph_range.EndPosition());
+  if (paragraph_length <= kHotModeChunkSize)
+    return paragraph_range;
+
+  // Otherwise, check a chunk of text centered at |position|.
   TextIteratorBehavior behavior = TextIteratorBehavior::Builder()
                                       .SetEmitsObjectReplacementCharacter(true)
                                       .Build();
   BackwardsCharacterIterator backward_iterator(full_range.StartPosition(),
                                                position, behavior);
   if (!backward_iterator.AtEnd())
     backward_iterator.Advance(kHotModeChunkSize / 2);
   const Position& chunk_start = backward_iterator.EndPosition();
   CharacterIterator forward_iterator(position, full_range.EndPosition(),
                                      behavior);
@@ skipping 28 matching lines @@
         current_word, DocumentMarker::MisspellingMarkers());
     return;
   }
 
   const EphemeralRange& checking_range =
       CalculateHotModeCheckingRange(*root_editable, position);
   requester_->RequestCheckingFor(checking_range);
 }
 
 }  // namespace blink