Implement support for expanding crop rects in image filters

tests/ImageFilterTest.cpp

Index: tests/ImageFilterTest.cpp
diff --git a/tests/ImageFilterTest.cpp b/tests/ImageFilterTest.cpp
index f730e1e2411c464f301b4711f4b1c10a2a0375dc..97d3d0fbfb353210d2a1d7663e06759a589174ae 100644
--- a/tests/ImageFilterTest.cpp
+++ b/tests/ImageFilterTest.cpp
@@ -246,7 +246,7 @@ static void test_crop_rects(SkBaseDevice* device, skiatest::Reporter* reporter)
         SkIPoint offset;
         SkString str;
         str.printf("filter %d", static_cast<int>(i));
-        SkImageFilter::Context ctx(SkMatrix::I(), SkIRect::MakeEmpty());
+        SkImageFilter::Context ctx(SkMatrix::I(), SkIRect::MakeLargest());
         REPORTER_ASSERT_MESSAGE(reporter, filter->filterImage(&proxy, bitmap, ctx, &result, &offset), str.c_str());
         REPORTER_ASSERT_MESSAGE(reporter, offset.fX == 20 && offset.fY == 30, str.c_str());
     }