Track the region where text is painted.

Source/core/platform/graphics/skia/PlatformContextSkia.cpp

Index: Source/core/platform/graphics/skia/PlatformContextSkia.cpp
diff --git a/Source/core/platform/graphics/skia/PlatformContextSkia.cpp b/Source/core/platform/graphics/skia/PlatformContextSkia.cpp
index f0fe9b1fe42947f523aa98ff1be4ace68c89f41d..347372fe5c37ca683040f8ef4246bf12cecf8b3f 100644
--- a/Source/core/platform/graphics/skia/PlatformContextSkia.cpp
+++ b/Source/core/platform/graphics/skia/PlatformContextSkia.cpp
@@ -68,6 +68,7 @@ PlatformContextSkia::PlatformContextSkia(SkCanvas* canvas)
     : m_canvas(canvas)
     , m_deferredSaveFlags(0)
     , m_trackOpaqueRegion(false)
+    , m_trackTextRegion(false)
     , m_printing(false)
     , m_accelerated(false)
     , m_drawingToImageBuffer(false)
@@ -493,4 +494,12 @@ bool PlatformContextSkia::couldUseLCDRenderedText()
     return m_gc->shouldSmoothFonts();
 }
 
+void PlatformContextSkia::didDrawTextInRect(const SkRect& textRect)
+{
+    if (m_trackTextRegion) {
+        TRACE_EVENT0("skia", "PlatformContextSkia::trackTextRegion");
+        m_textRegion.join(textRect);
+    }
+}
+
 } // namespace WebCore