Track the region where text is painted.

Source/core/platform/graphics/FontFastPath.cpp

Index: Source/core/platform/graphics/FontFastPath.cpp
diff --git a/Source/core/platform/graphics/FontFastPath.cpp b/Source/core/platform/graphics/FontFastPath.cpp
index e4019f001badf8b7a9bb15eeff42937fd3fe776e..691b0f2f228f5d618ef4ae96ab54f81e96800784 100644
--- a/Source/core/platform/graphics/FontFastPath.cpp
+++ b/Source/core/platform/graphics/FontFastPath.cpp
@@ -443,7 +443,7 @@ float Font::getGlyphsAndAdvancesForSimpleText(const TextRun& run, int from, int
     return initialAdvance;
 }
 
-void Font::drawSimpleText(GraphicsContext* context, const TextRun& run, const FloatPoint& point, int from, int to) const
+void Font::drawSimpleText(GraphicsContext* context, const TextRun& run, const FloatPoint& point, const FloatRect& textRect, int from, int to) const
 {
     // This glyph buffer holds our glyphs+advances+font data for each glyph.
     GlyphBuffer glyphBuffer;
@@ -454,10 +454,10 @@ void Font::drawSimpleText(GraphicsContext* context, const TextRun& run, const Fl
         return;
 
     FloatPoint startPoint(startX, point.y());
-    drawGlyphBuffer(context, run, glyphBuffer, startPoint);
+    drawGlyphBuffer(context, run, glyphBuffer, startPoint, textRect);
 }
 
-void Font::drawEmphasisMarksForSimpleText(GraphicsContext* context, const TextRun& run, const AtomicString& mark, const FloatPoint& point, int from, int to) const
+void Font::drawEmphasisMarksForSimpleText(GraphicsContext* context, const TextRun& run, const AtomicString& mark, const FloatPoint& point, const FloatRect& textRect, int from, int to) const
 {
     GlyphBuffer glyphBuffer;
     float initialAdvance = getGlyphsAndAdvancesForSimpleText(run, from, to, glyphBuffer, ForTextEmphasis);
@@ -465,10 +465,10 @@ void Font::drawEmphasisMarksForSimpleText(GraphicsContext* context, const TextRu
     if (glyphBuffer.isEmpty())
         return;
 
-    drawEmphasisMarks(context, run, glyphBuffer, mark, FloatPoint(point.x() + initialAdvance, point.y()));
+    drawEmphasisMarks(context, run, glyphBuffer, mark, FloatPoint(point.x() + initialAdvance, point.y()), textRect);
 }
 
-void Font::drawGlyphBuffer(GraphicsContext* context, const TextRun& run, const GlyphBuffer& glyphBuffer, const FloatPoint& point) const
+void Font::drawGlyphBuffer(GraphicsContext* context, const TextRun& run, const GlyphBuffer& glyphBuffer, const FloatPoint& point, const FloatRect& textRect) const
 {   
 #if !ENABLE(SVG_FONTS)
     UNUSED_PARAM(run);
@@ -494,7 +494,7 @@ void Font::drawGlyphBuffer(GraphicsContext* context, const TextRun& run, const G
                 renderingContext->drawSVGGlyphs(context, run, fontData, glyphBuffer, lastFrom, nextGlyph - lastFrom, startPoint);
             else
 #endif
-                drawGlyphs(context, fontData, glyphBuffer, lastFrom, nextGlyph - lastFrom, startPoint);
+                drawGlyphs(context, fontData, glyphBuffer, lastFrom, nextGlyph - lastFrom, startPoint, textRect);
 
             lastFrom = nextGlyph;
             fontData = nextFontData;
@@ -510,7 +510,7 @@ void Font::drawGlyphBuffer(GraphicsContext* context, const TextRun& run, const G
         renderingContext->drawSVGGlyphs(context, run, fontData, glyphBuffer, lastFrom, nextGlyph - lastFrom, startPoint);
     else
 #endif
-        drawGlyphs(context, fontData, glyphBuffer, lastFrom, nextGlyph - lastFrom, startPoint);
+        drawGlyphs(context, fontData, glyphBuffer, lastFrom, nextGlyph - lastFrom, startPoint, textRect);
 }
 
 inline static float offsetToMiddleOfGlyph(const SimpleFontData* fontData, Glyph glyph)
@@ -528,7 +528,7 @@ inline static float offsetToMiddleOfGlyphAtIndex(const GlyphBuffer& glyphBuffer,
     return offsetToMiddleOfGlyph(glyphBuffer.fontDataAt(i), glyphBuffer.glyphAt(i));
 }
 
-void Font::drawEmphasisMarks(GraphicsContext* context, const TextRun& run, const GlyphBuffer& glyphBuffer, const AtomicString& mark, const FloatPoint& point) const
+void Font::drawEmphasisMarks(GraphicsContext* context, const TextRun& run, const GlyphBuffer& glyphBuffer, const AtomicString& mark, const FloatPoint& point, const FloatRect& textRect) const
 {
     FontCachePurgePreventer purgePreventer;
     
@@ -556,7 +556,7 @@ void Font::drawEmphasisMarks(GraphicsContext* context, const TextRun& run, const
     }
     markBuffer.add(glyphBuffer.glyphAt(glyphBuffer.size() - 1) ? markGlyph : spaceGlyph, markFontData, 0);
 
-    drawGlyphBuffer(context, run, markBuffer, startPoint);
+    drawGlyphBuffer(context, run, markBuffer, startPoint, textRect);
 }
 
 float Font::floatWidthForSimpleText(const TextRun& run, HashSet<const SimpleFontData*>* fallbackFonts, GlyphOverflow* glyphOverflow) const