Implement a persistent uniqueID-based cache for SkImageFilter.

tests/ImageFilterTest.cpp

Index: tests/ImageFilterTest.cpp
diff --git a/tests/ImageFilterTest.cpp b/tests/ImageFilterTest.cpp
index 7da4a911ef37c821d6da9c61808fe1ee61b51b3e..0766c15edfa6e460ae3bc5700b88254569e15acd 100644
--- a/tests/ImageFilterTest.cpp
+++ b/tests/ImageFilterTest.cpp
@@ -262,8 +262,7 @@ static void test_crop_rects(SkBaseDevice* device, skiatest::Reporter* reporter)
         SkIPoint offset;
         SkString str;
         str.printf("filter %d", static_cast<int>(i));
-        SkAutoTUnref<SkImageFilter::Cache> cache(SkImageFilter::Cache::Create(2));
-        SkImageFilter::Context ctx(SkMatrix::I(), SkIRect::MakeLargest(), cache.get());
+        SkImageFilter::Context ctx(SkMatrix::I(), SkIRect::MakeLargest(), NULL);
         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());