Expose a Paragraph.getWordBoundary method to dart. (#2675)

* Expose a Paragraph.getWordBoundary method to dart.

Used by text selection to select a word.

sky/engine/core/dart/text.dart

@@ -674,6 +674,13 @@ abstract class Paragraph extends NativeFieldWrapperClass2 {
     return new TextPosition(offset: encoded[0], affinity: TextAffinity.values[encoded[1]]);
   }
   List<int> _getPositionForOffset(Offset offset) native "Paragraph_getPositionForOffset";
+
+  /// Returns the [start, end] of the word at the given offset. Characters not
+  /// part of a word, such as spaces, symbols, and punctuation, have word breaks
+  /// on both sides. In such cases, this method will return [offset, offset+1].
+  /// Word boundaries are defined more precisely in Unicode Standard Annex #29
+  /// http://www.unicode.org/reports/tr29/#Word_Boundaries
+  List<int> getWordBoundary(int offset) native "Paragraph_getWordBoundary";
 }
 
 /// Builds a [Paragraph] containing text with the given styling information.

sky/engine/core/text/Paragraph.cpp

@@ -11,6 +11,7 @@
 #include "sky/engine/core/rendering/style/RenderStyle.h"
 #include "sky/engine/platform/fonts/FontCache.h"
 #include "sky/engine/platform/graphics/GraphicsContext.h"
+#include "sky/engine/platform/text/TextBoundaries.h"
 #include "sky/engine/public/platform/Platform.h"
 #include "sky/engine/tonic/dart_args.h"
 #include "sky/engine/tonic/dart_binding_macros.h"
@@ -29,6 +30,7 @@ IMPLEMENT_WRAPPERTYPEINFO(ui, Paragraph);
   V(Paragraph, alphabeticBaseline) \
   V(Paragraph, ideographicBaseline) \
   V(Paragraph, layout) \
+  V(Paragraph, getWordBoundary) \
   V(Paragraph, getRectsForRange) \
   V(Paragraph, getPositionForOffset)
 
@@ -153,4 +155,27 @@ Dart_Handle Paragraph::getPositionForOffset(const Offset& offset) {
   return result;
 }
 
+Dart_Handle Paragraph::getWordBoundary(unsigned offset) {
+  String text;
+  int start, end;
+
+  for (RenderObject* object = m_renderView.get(); object; object = object->nextInPreOrder()) {
+    if (!object->isText())
+      continue;
+    RenderText* renderText = toRenderText(object);
+    text.append(renderText->text());
+  }
+
+  TextBreakIterator* it = wordBreakIterator(text, 0, text.length());
+  end = it->following(offset);
+  if (end < 0)
+      end = it->last();
+  start = it->previous();
+
+  Dart_Handle result = Dart_NewList(2);
+  Dart_ListSetAt(result, 0, ToDart(start));
+  Dart_ListSetAt(result, 1, ToDart(end));
+  return result;
+}
+
 } // namespace blink

sky/engine/core/text/Paragraph.h

@@ -37,6 +37,7 @@ public:
 
     std::vector<TextBox> getRectsForRange(unsigned start, unsigned end);
     Dart_Handle getPositionForOffset(const Offset& offset);
+    Dart_Handle getWordBoundary(unsigned offset);
 
     RenderView* renderView() const { return m_renderView.get(); }