cc/viz: Remove PaintFilter::ToString.

R=enne@chromium.org

Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: Iac62262f6c09fcfd9877b9fafca0bf7a3cb30545
Reviewed-on: https://chromium-review.googlesource.com/1076771
Reviewed-by: enne <enne@chromium.org>
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Commit-Queue: Khushal <khushalsagar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#562522}

cc/paint/paint_filter.h

@@ -93,14 +93,6 @@ class CC_PAINT_EXPORT PaintFilter : public SkRefCnt {
       return 0;
     return cached_sk_filter_->countInputs();
   }
-  std::string ToString() const {
-    if (!cached_sk_filter_)
-      return "Invalid filter";
-
-    SkString str;
-    cached_sk_filter_->toString(&str);
-    return str.c_str();
-  }
   const CropRect* crop_rect() const {
     return base::OptionalOrNullptr(crop_rect_);
   }

services/viz/public/cpp/compositing/struct_traits_unittest.cc

@@ -165,8 +165,10 @@ void ExpectEqual(const cc::FilterOperation& input,
       EXPECT_EQ(input.zoom_inset(), output.zoom_inset());
       break;
     case cc::FilterOperation::REFERENCE: {
-      EXPECT_EQ(input.image_filter()->ToString(),
-                output.image_filter()->ToString());
+      ASSERT_EQ(!!input.image_filter(), !!output.image_filter());
+      if (input.image_filter()) {
+        EXPECT_EQ(*input.image_filter(), *output.image_filter());
+      }
       break;
     }
     case cc::FilterOperation::ALPHA_THRESHOLD: