Use binary search in ShapeResult::InsertRun

Text shaping processes runs according to font fallback and produces out-
of-sequence text runs. These runs then need to be sorted in visual order
and that happens in ShapeResult::InsertRun by linearly scanning previous
runs until the appropriate insert location is identified. This is rather
slow and inefficient, especially for large blocks of plain text content.

This patch replaces the linear scan with a more efficient binary search.

Bug: 981518
Change-Id: I781c768a7f6d129c2998e725e9c889332eb43675
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1695756
Commit-Queue: Emil A Eklund <eae@chromium.org>
Commit-Queue: Koji Ishii <kojii@chromium.org>
Reviewed-by: Koji Ishii <kojii@chromium.org>
Cr-Commit-Position: refs/heads/master@{#676241}

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

@@ -1114,24 +1114,26 @@ void ShapeResult::InsertRun(scoped_refptr<ShapeResult::RunInfo> run_to_insert,
 
 void ShapeResult::InsertRun(scoped_refptr<ShapeResult::RunInfo> run) {
   // The runs are stored in result->m_runs in visual order. For LTR, we place
-  // the run to be inserted before the next run with a bigger character
-  // start index. For RTL, we place the run before the next run with a lower
-  // character index. Otherwise, for both directions, at the end.
-  if (HB_DIRECTION_IS_FORWARD(run->direction_)) {
-    for (wtf_size_t pos = 0; pos < runs_.size(); ++pos) {
-      if (runs_.at(pos)->start_index_ > run->start_index_) {
-        runs_.insert(pos, std::move(run));
-        break;
-      }
-    }
-  } else {
-    for (wtf_size_t pos = 0; pos < runs_.size(); ++pos) {
-      if (runs_.at(pos)->start_index_ < run->start_index_) {
-        runs_.insert(pos, std::move(run));
-        break;
-      }
-    }
-  }
+  // the run to be inserted before the next run with a bigger character start
+  // index.
+  const auto ltr_comparer = [](scoped_refptr<RunInfo>& run,
+                               unsigned start_index) {
+    return run->start_index_ < start_index;
+  };
+
+  // For RTL, we place the run before the next run with a lower character
+  // index. Otherwise, for both directions, at the end.
+  const auto rtl_comparer = [](scoped_refptr<RunInfo>& run,
+                               unsigned start_index) {
+    return run->start_index_ > start_index;
+  };
+
+  Vector<scoped_refptr<RunInfo>>::iterator iterator = std::lower_bound(
+      runs_.begin(), runs_.end(), run->start_index_,
+      HB_DIRECTION_IS_FORWARD(run->direction_) ? ltr_comparer : rtl_comparer);
+  if (iterator != runs_.end())
+    runs_.insert(iterator - runs_.begin(), std::move(run));
+
   // If we didn't find an existing slot to place it, append.
   if (run)
     runs_.push_back(std::move(run));