Revert "remove toString"

This reverts commit 5191880cbf3ee4d122b0d11b4945fbab0784fda7.

Reason for revert: broke flutter

Original change's description:
> remove toString
> 
> toString may have been used by obsolete debugger only
> find out if that is so
> 
> R=​brianosman@google.com,bsalomon@google.com
> 
> Docs-Preview: https://skia.org/?cl=119894
> Bug:830651
> Change-Id: I737f19b7d3fbc869bea2f443fa3b5ed7c1393ffd
> Reviewed-on: https://skia-review.googlesource.com/119894
> Commit-Queue: Cary Clark <caryclark@google.com>
> Reviewed-by: Brian Salomon <bsalomon@google.com>

TBR=bsalomon@google.com,brianosman@google.com,caryclark@google.com,caryclark@skia.org

Change-Id: I9f81de6c3615ee0608bcea9081b77239b4b8816c
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 830651
Reviewed-on: https://skia-review.googlesource.com/129340
Reviewed-by: Cary Clark <caryclark@google.com>
Commit-Queue: Cary Clark <caryclark@google.com>

1 files changed, 12 insertions, 0 deletions

diff --git a/gm/imagefiltersbase.cpp b/gm/imagefiltersbase.cpp
index d1a324a118..5432dee2a1 100644
--- a/gm/imagefiltersbase.cpp
+++ b/gm/imagefiltersbase.cpp
@@ -32,6 +32,7 @@ public:
         return sk_sp<SkImageFilter>(new FailImageFilter);
     }
 
+    void toString(SkString* str) const override;
     SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS(FailImageFilter)
 
 protected:
@@ -56,6 +57,11 @@ sk_sp<SkFlattenable> FailImageFilter::CreateProc(SkReadBuffer& buffer) {
     return FailImageFilter::Make();
 }
 
+void FailImageFilter::toString(SkString* str) const {
+    str->appendf("FailImageFilter: (");
+    str->append(")");
+}
+
 class IdentityImageFilter : public SkImageFilter {
 public:
     class Registrar {
@@ -70,6 +76,7 @@ public:
         return sk_sp<SkImageFilter>(new IdentityImageFilter(std::move(input)));
     }
 
+    void toString(SkString* str) const override;
     SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS(IdentityImageFilter)
 
 protected:
@@ -95,6 +102,11 @@ sk_sp<SkFlattenable> IdentityImageFilter::CreateProc(SkReadBuffer& buffer) {
     return IdentityImageFilter::Make(common.getInput(0));
 }
 
+void IdentityImageFilter::toString(SkString* str) const {
+    str->appendf("IdentityImageFilter: (");
+    str->append(")");
+}
+
 ///////////////////////////////////////////////////////////////////////////////
 
 static void draw_paint(SkCanvas* canvas, const SkRect& r, sk_sp<SkImageFilter> imf) {