Fix HarfBuzzShaperTest::SafeToBreakMissingRun

This test was added when we found Mac produces rare
ShapeResult, by constructing the same run/glyph data
artificially.

During tweaking the tests, a character was added to runs,
but forgot to update the NumCharacters(), which made
Start/EndIndexForResult() incorrect.

This patch fixes that, and also add CheckConsistency() and
two new EXPECT() to ensure the aritificially built
ShapeResult is good.

Bug: 636993
Cq-Include-Trybots: luci.chromium.try:linux_layout_tests_layout_ng
Change-Id: Iea0189f370f9e3d4546f33582f6ad363929511cc
Reviewed-on: https://chromium-review.googlesource.com/1100599Reviewed-by: Emil A Eklund <eae@chromium.org>
Commit-Queue: Emil A Eklund <eae@chromium.org>
Cr-Commit-Position: refs/heads/master@{#567332}

third_party/blink/renderer/platform/fonts/shaping/harf_buzz_shaper_test.cc

@@ -1234,11 +1234,17 @@ TEST_F(HarfBuzzShaperTest, DISABLED_SafeToBreakArabicCommonLigatures) {
 // RTL on Mac may not have runs for all characters. crbug.com/774034
 TEST_P(ShapeParameterTest, SafeToBreakMissingRun) {
   TextDirection direction = GetParam();
-  scoped_refptr<ShapeResult> result = ShapeResult::Create(&font, 7, direction);
+  scoped_refptr<ShapeResult> result = ShapeResult::Create(&font, 8, direction);
   result->InsertRunForTesting(2, 1, direction, {0});
   result->InsertRunForTesting(3, 3, direction, {0, 1});
-  // The character index 7 is missing.
+  // The character index 6 and 7 is missing.
   result->InsertRunForTesting(8, 2, direction, {0});
+#if DCHECK_IS_ON()
+  result->CheckConsistency();
+#endif
+
+  EXPECT_EQ(2u, result->StartIndexForResult());
+  EXPECT_EQ(10u, result->EndIndexForResult());
 
   EXPECT_EQ(2u, result->NextSafeToBreakOffset(2));
   EXPECT_EQ(3u, result->NextSafeToBreakOffset(3));

third_party/blink/renderer/platform/fonts/shaping/shape_result.cc

@@ -821,6 +821,7 @@ ShapeResult::RunInfo* ShapeResult::InsertRunForTesting(
   // RTL runs have glyphs in the descending order of character_index.
   if (Rtl())
     run->glyph_data_.Reverse();
+  num_glyphs_ += run->NumGlyphs();
   RunInfo* run_ptr = run.get();
   InsertRun(std::move(run));
   return run_ptr;
@@ -1013,24 +1014,28 @@ void ShapeResult::CheckConsistency() const {
     return;
   }
 
-  unsigned index = StartIndexForResult();
+  const unsigned start_index = StartIndexForResult();
+  unsigned index = start_index;
   unsigned num_glyphs = 0;
   if (!Rtl()) {
     for (const auto& run : runs_) {
-      DCHECK_EQ(index, run->start_index_);
-      index += run->num_characters_;
+      // Characters maybe missing, but must be in increasing order.
+      DCHECK_GE(run->start_index_, index);
+      index = run->start_index_ + run->num_characters_;
       num_glyphs += run->glyph_data_.size();
     }
   } else {
     // RTL on Mac may not have runs for the all characters. crbug.com/774034
     index = runs_.back()->start_index_;
     for (const auto& run : base::Reversed(runs_)) {
-      DCHECK_EQ(index, run->start_index_);
-      index += run->num_characters_;
+      DCHECK_GE(run->start_index_, index);
+      index = run->start_index_ + run->num_characters_;
       num_glyphs += run->glyph_data_.size();
     }
   }
-  DCHECK_EQ(index, EndIndexForResult());
+  const unsigned end_index = EndIndexForResult();
+  DCHECK_LE(index, end_index);
+  DCHECK_EQ(end_index - start_index, num_characters_);
   DCHECK_EQ(num_glyphs, num_glyphs_);
 }
 #endif