Introduce TextBuffer as Output Type of copyTextTo() for Text Iterators

third_party/WebKit/Source/core/editing/VisibleUnits.cpp

Index: third_party/WebKit/Source/core/editing/VisibleUnits.cpp
diff --git a/third_party/WebKit/Source/core/editing/VisibleUnits.cpp b/third_party/WebKit/Source/core/editing/VisibleUnits.cpp
index 358c9b1ae37eaa29b6eab16bc94b8caa69b7b1c1..608c7a8930a09407150b2b42390d8c7caf9b8fe2 100644
--- a/third_party/WebKit/Source/core/editing/VisibleUnits.cpp
+++ b/third_party/WebKit/Source/core/editing/VisibleUnits.cpp
@@ -666,16 +666,17 @@ static VisiblePositionTemplate<Strategy> previousBoundary(const VisiblePositionT
     const PositionTemplate<Strategy> start = PositionTemplate<Strategy>::editingPositionOf(boundary, 0).parentAnchoredEquivalent();
     const PositionTemplate<Strategy> end = pos.parentAnchoredEquivalent();
 
-    Vector<UChar, 1024> string;
+    ForwardsTextBuffer suffixString;
     unsigned suffixLength = 0;
 
     if (requiresContextForWordBoundary(characterBefore(c))) {
         TextIteratorAlgorithm<Strategy> forwardsIterator(end, PositionTemplate<Strategy>::afterNode(boundary));
         while (!forwardsIterator.atEnd()) {
-            Vector<UChar, 1024> characters;
+            // TODO(xiaochengh): Eliminate this intermediate buffer.
+            ForwardsTextBuffer characters;
             forwardsIterator.copyTextTo(characters);
             int i = endOfFirstWordBoundaryContext(characters.data(), characters.size());
-            string.append(characters.data(), i);
+            suffixString.pushRange(characters.data(), i);
             suffixLength += i;
             if (static_cast<unsigned>(i) < characters.size())
                 break;
@@ -683,6 +684,9 @@ static VisiblePositionTemplate<Strategy> previousBoundary(const VisiblePositionT
         }
     }
 
+    BackwardsTextBuffer string;
+    string.pushRange(suffixString.data(), suffixString.size());
+
     SimplifiedBackwardsTextIteratorAlgorithm<Strategy> it(start, end);
     unsigned next = 0;
     bool needMoreContext = false;
@@ -690,16 +694,12 @@ static VisiblePositionTemplate<Strategy> previousBoundary(const VisiblePositionT
         bool inTextSecurityMode = it.isInTextSecurityMode();
         // iterate to get chunks until the searchFunction returns a non-zero
         // value.
-        // TODO(xiaochengh): Iterative prepending has quadratic running time
-        // in the worst case. Should improve it to linear.
         if (!inTextSecurityMode) {
             it.copyTextTo(string);
         } else {
             // Treat bullets used in the text security mode as regular
             // characters when looking for boundaries
-            Vector<UChar, 1024> iteratorString;
-            iteratorString.fill('x', it.length());
-            string.prepend(iteratorString.data(), iteratorString.size());
+            string.pushCharacters('x', it.length());
         }
         // TODO(xiaochengh): The following line takes O(string.size()) time,
         // which makes the while loop take quadratic time in the worst case.
@@ -746,19 +746,18 @@ static VisiblePositionTemplate<Strategy> nextBoundary(const VisiblePositionTempl
     Document& d = boundary->document();
     const PositionTemplate<Strategy> start(pos.parentAnchoredEquivalent());
 
-    Vector<UChar, 1024> string;
+    BackwardsTextBuffer prefixString;
     unsigned prefixLength = 0;
 
     if (requiresContextForWordBoundary(characterAfter(c))) {
         SimplifiedBackwardsTextIteratorAlgorithm<Strategy> backwardsIterator(PositionTemplate<Strategy>::firstPositionInNode(&d), start);
         while (!backwardsIterator.atEnd()) {
-            Vector<UChar, 1024> characters;
+            // TODO(xiaochengh): Eliminate this intermediate buffer.
+            BackwardsTextBuffer characters;
             backwardsIterator.copyTextTo(characters);
             int length = characters.size();
             int i = startOfLastWordBoundaryContext(characters.data(), length);
-            // TODO(xiaochengh): Iterative prepending has quadratic running
-            // time in the worst case. Should improve it to linear.
-            string.prepend(characters.data() + i, length - i);
+            prefixString.pushRange(characters.data() + i, length - i);
             prefixLength += length - i;
             if (i > 0)
                 break;
@@ -766,6 +765,9 @@ static VisiblePositionTemplate<Strategy> nextBoundary(const VisiblePositionTempl
         }
     }
 
+    ForwardsTextBuffer string;
+    string.pushRange(prefixString.data(), prefixString.size());
+
     const PositionTemplate<Strategy> searchStart = PositionTemplate<Strategy>::editingPositionOf(start.anchorNode(), start.offsetInContainerNode());
     const PositionTemplate<Strategy> searchEnd = PositionTemplate<Strategy>::lastPositionInNode(boundary);
     TextIteratorAlgorithm<Strategy> it(searchStart, searchEnd, TextIteratorEmitsCharactersBetweenAllVisiblePositions);
@@ -783,9 +785,7 @@ static VisiblePositionTemplate<Strategy> nextBoundary(const VisiblePositionTempl
         } else {
             // Treat bullets used in the text security mode as regular
             // characters when looking for boundaries
-            Vector<UChar, 1024> iteratorString;
-            iteratorString.fill('x', it.length());
-            string.append(iteratorString.data(), iteratorString.size());
+            string.pushCharacters('x', it.length());
         }
         next = searchFunction(string.data(), string.size(), offset, MayHaveMoreContext, needMoreContext);
         if (next != string.size())