Introduce TextAccumulator for Progressive Extraction from Text Iterators

third_party/WebKit/Source/core/editing/iterators/ExponentialAccumulator.h

Index: third_party/WebKit/Source/core/editing/iterators/ExponentialAccumulator.h
diff --git a/third_party/WebKit/Source/core/editing/iterators/ExponentialAccumulator.h b/third_party/WebKit/Source/core/editing/iterators/ExponentialAccumulator.h
new file mode 100644
index 0000000000000000000000000000000000000000..800b30e05e5b24ad2d9005660a71f5f07c6f4560
--- /dev/null
+++ b/third_party/WebKit/Source/core/editing/iterators/ExponentialAccumulator.h
@@ -0,0 +1,29 @@
+// Copyright 2016 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.
+
+#ifndef ExponentialAccumulator_h
+#define ExponentialAccumulator_h
+
+#include "core/CoreExport.h"

[yosin_UTC9, 2016/02/15 05:58:30]

nit: Since nothing to export, we don't need to include "CoreExport.h"

+
+namespace blink {
+
+class ExponentialAccumulator {

[yosin_UTC9, 2016/02/15 05:58:30]

|ExponentialAccumulator| does accumulate nothing. It is counter.
Do you want to make this class as base class of |BackwardsTextBuffer| and
|ForwardsTextBuffer|?

Or template class?

template <typename TextBuffer>
class ExponentialAccumulator {
  const UChar* data() const { return m_buffer.data() }
  int capacity() const { return m_buffer.capacity(); }
  int size() const { return m_buffer.size(); }

  void push(TextIterator* it) {
     int accumulated = it.copyTextTo(&m_buffer, size(), capacity());
     m_size += accumulated;
  }

  void enlarge() { m_buffer.enlarge(); }

  TextBuffer m_buffer;
};

static VisiblePositionTemplate<Strategy> previousBoundary(...) {
  ...
  ExponentialAccumulator<BackwardsTextBuffer> accumulator;
  ...

  if (!inTextSecurityMode) {
    while (!next && accumulator.size() < it.length()) {
      accumulator.push(&it);
      next = searchFunction(accumulator.data(), accumulator.size(),
accumulaotr.size() - suffixLength, MayHaveMoreContext,   needMoreContext);
      if (next)
         break;
      // |it| hold characters more than |accumulator| buffer, we enlarge
|accumulator| to hold more characters.
      accumulator.enlarge();
    }
  } else {
    accumulator.pushCharacters('x', it.length());
    next = 0;
  }
  it.advance();
  accumulator.rest();
}

+    STACK_ALLOCATED();
+    WTF_MAKE_NONCOPYABLE(ExponentialAccumulator);
+public:
+    ExponentialAccumulator() {}
+    int size() const { return m_size; }
+    int capacity() const { return m_capacity; }
+    void reset() { m_size = 0; }
+    void grow(int delta) { m_size += delta; m_capacity += delta; }

[yosin_UTC9, 2016/02/15 05:58:30]

nit: enlarge() is better name?
nit: Don't have two statements in a line.

+
+private:
+    int m_size = 0;
+    int m_capacity = 1024;
+};
+
+} // namespace blink
+
+#endif // ExponentialAccumulator_h