Implement canComputeFastBounds() for image filters.

gm/colorfilterimagefilter.cpp

Index: gm/colorfilterimagefilter.cpp
diff --git a/gm/colorfilterimagefilter.cpp b/gm/colorfilterimagefilter.cpp
index b34058f9d74d3c2aba6e6caf9ca8a68d2194e07d..500450f61bd9687d33abc24955c216f18edd38f3 100644
--- a/gm/colorfilterimagefilter.cpp
+++ b/gm/colorfilterimagefilter.cpp
@@ -45,7 +45,7 @@ static SkImageFilter* make_grayscale(SkImageFilter* input = NULL) {
 
 static SkImageFilter* make_mode_blue(SkImageFilter* input = NULL) {
     SkAutoTUnref<SkColorFilter> filter(
-        SkColorFilter::CreateModeFilter(SK_ColorBLUE, SkXfermode::kSrcIn_Mode));
+        SkColorFilter::CreateModeFilter(SK_ColorBLUE, SkXfermode::kSrc_Mode));
     return SkColorFilterImageFilter::Create(filter, input);
 }
 
@@ -120,6 +120,12 @@ protected:
             drawClippedRect(canvas, r, paint, 3);
             canvas->translate(FILTER_WIDTH + MARGIN, 0);
         }
+        {
+            SkAutoTUnref<SkImageFilter> blue(make_mode_blue());
+            paint.setImageFilter(blue.get());
+            drawClippedRect(canvas, r, paint, 5);
+            canvas->translate(FILTER_WIDTH + MARGIN, 0);
+        }
     }
 
 private: