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 3cbf7cdd5a7bfab347fdd7fe07ae5a1f1c5d7c3d..ea336fcafcf4e478fe1e1a5db4a8236c0881ff36 100644
--- a/Source/core/platform/graphics/skia/PlatformContextSkia.cpp
+++ b/Source/core/platform/graphics/skia/PlatformContextSkia.cpp
@@ -189,6 +189,7 @@ 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)
@@ -614,4 +615,12 @@ bool PlatformContextSkia::couldUseLCDRenderedText()
     return m_gc->shouldSmoothFonts();
 }
 
+void PlatformContextSkia::trackTextRegion(const SkRect& textRect)
+{
+    if (m_trackTextRegion) {
+        TRACE_EVENT0("skia", "PlatformContextSkia::trackTextRegion");
+        m_textRegion.join(textRect);

[eseidel, 2013/04/18 21:04:38]

I hope this isn't a WebCore::Region (which is abysmally slow)

[alokp, 2013/04/18 22:22:37]

Not WebCore::Region. It is SkRect (for now). I may need a tighter low-cost
region in future, so keeping the name generic.

+    }
+}
+
 } // namespace WebCore