Add support for letterSpacing

sky/engine/core/dart/text.dart

@@ -126,7 +126,8 @@ Int32List _encodeTextStyle(Color color,
                            FontWeight fontWeight,
                            FontStyle fontStyle,
                            String fontFamily,
-                           double fontSize) {
+                           double fontSize,
+                           double letterSpacing) {
   Int32List result = new Int32List(7);
   if (color != null) {
     result[0] |= 1 << 1;
@@ -164,6 +165,10 @@ Int32List _encodeTextStyle(Color color,
     result[0] |= 1 << 8;
     // Passed separately to native.
   }
+  if (letterSpacing != null) {
+    result[0] |= 1 << 9;
+    // Passed separately to native.
+  }
   return result;
 }
 
@@ -176,7 +181,8 @@ class TextStyle {
     FontWeight fontWeight,
     FontStyle fontStyle,
     String fontFamily,
-    double fontSize
+    double fontSize,
+    double letterSpacing
   }) : _encoded = _encodeTextStyle(color,
                                    decoration,
                                    decorationColor,
@@ -184,13 +190,16 @@ class TextStyle {
                                    fontWeight,
                                    fontStyle,
                                    fontFamily,
-                                   fontSize),
+                                   fontSize,
+                                   letterSpacing),
        _fontFamily = fontFamily ?? '',
-       _fontSize = fontSize;
+       _fontSize = fontSize,
+       _letterSpacing = letterSpacing;
 
   final Int32List _encoded;
   final String _fontFamily;
   final double _fontSize;
+  final double _letterSpacing;
 }
 
 // This encoding must match the C++ version ParagraphBuilder::build.
@@ -238,7 +247,7 @@ class ParagraphStyle {
 
 class ParagraphBuilder extends _ParagraphBuilder {
   void pushStyle(TextStyle style) {
-    _pushStyle(style._encoded, style._fontFamily, style._fontSize);
+    _pushStyle(style._encoded, style._fontFamily, style._fontSize, style._letterSpacing);
   }
 
   void pop() => _pop();

sky/engine/core/text/ParagraphBuilder.cpp

@@ -43,6 +43,7 @@ const int kFontWeightIndex = 5;
 const int kFontStyleIndex = 6;
 const int kFontFamilyIndex = 7;
 const int kFontSizeIndex = 8;
+const int kLetterSpacingIndex = 9;
 
 const int kColorMask = 1 << kColorIndex;
 const int kTextDecorationMask = 1 << kTextDecorationIndex;
@@ -52,6 +53,7 @@ const int kFontWeightMask = 1 << kFontWeightIndex;
 const int kFontStyleMask = 1 << kFontStyleIndex;
 const int kFontFamilyMask = 1 << kFontFamilyIndex;
 const int kFontSizeMask = 1 << kFontSizeIndex;
+const int kLetterSpacingMask = 1 << kLetterSpacingIndex;
 
 // ParagraphStyle
 
@@ -78,7 +80,7 @@ ParagraphBuilder::~ParagraphBuilder()
 {
 }
 
-void ParagraphBuilder::pushStyle(Int32List& encoded, const String& fontFamily, double fontSize)
+void ParagraphBuilder::pushStyle(Int32List& encoded, const String& fontFamily, double fontSize, double letterSpacing)
 {
     DCHECK(encoded.num_elements() == 7);
     RefPtr<RenderStyle> style = RenderStyle::create();
@@ -100,7 +102,7 @@ void ParagraphBuilder::pushStyle(Int32List& encoded, const String& fontFamily, d
     if (mask & kTextDecorationStyleMask)
       style->setTextDecorationStyle(static_cast<TextDecorationStyle>(encoded[kTextDecorationStyleIndex]));
 
-    if (mask & (kFontWeightMask | kFontStyleMask | kFontFamilyMask | kFontSizeMask)) {
+    if (mask & (kFontWeightMask | kFontStyleMask | kFontFamilyMask | kFontSizeMask | kLetterSpacingMask)) {
       FontDescription fontDescription = style->fontDescription();
 
       if (mask & kFontWeightMask)
@@ -115,12 +117,15 @@ void ParagraphBuilder::pushStyle(Int32List& encoded, const String& fontFamily, d
         fontDescription.setFamily(family);
       }
 
-      if (mask & kFontSizeMask)  {
+      if (mask & kFontSizeMask) {
         fontDescription.setSpecifiedSize(fontSize);
         fontDescription.setIsAbsoluteSize(true);
         fontDescription.setComputedSize(FontSize::getComputedSizeFromSpecifiedSize(true, fontSize));
       }
 
+      if (mask & kLetterSpacingMask)
+        fontDescription.setLetterSpacing(letterSpacing);
+
       style->setFontDescription(fontDescription);
       style->font().update(m_fontSelector);
     }

sky/engine/core/text/ParagraphBuilder.h

@@ -24,7 +24,7 @@ public:
 
     ~ParagraphBuilder() override;
 
-    void pushStyle(Int32List& encoded, const String& fontFamily, double fontSize);
+    void pushStyle(Int32List& encoded, const String& fontFamily, double fontSize, double letterSpacing);
     void pop();
 
     void addText(const String& text);

sky/engine/core/text/ParagraphBuilder.idl

@@ -6,7 +6,7 @@
   Constructor(),
   PrivateDart,
 ] interface ParagraphBuilder {
-  void pushStyle(Int32List encoded, DOMString fontFamily, double fontSize);
+  void pushStyle(Int32List encoded, DOMString fontFamily, double fontSize, double letterSpacing);
   void pop();
 
   void addText(DOMString text);