Add toString methods to SkImageFilter-derived classes

src/effects/SkDisplacementMapEffect.cpp

Index: src/effects/SkDisplacementMapEffect.cpp
diff --git a/src/effects/SkDisplacementMapEffect.cpp b/src/effects/SkDisplacementMapEffect.cpp
index b1f6a97e7147ac4e84f58bca0b584974f62347c4..2c7f5ee8cee5b9e71217a886d10af662cbbaf3fb 100644
--- a/src/effects/SkDisplacementMapEffect.cpp
+++ b/src/effects/SkDisplacementMapEffect.cpp
@@ -281,6 +281,22 @@ bool SkDisplacementMapEffect::onFilterBounds(const SkIRect& src, const SkMatrix&
     return true;
 }
 
+#ifndef SK_IGNORE_TO_STRING
+void SkDisplacementMapEffect::toString(SkString* str) const {
+    str->appendf("SkDisplacementMapEffect: (");
+    str->appendf("scale: %f ", fScale);
+    str->appendf("displacement: (");
+    if (this->getDisplacementInput()) {
+        this->getDisplacementInput()->toString(str);
+    }
+    str->appendf(") color: (");
+    if (this->getColorInput()) {
+        this->getColorInput()->toString(str);
+    }
+    str->appendf("))");
+}
+#endif
+
 ///////////////////////////////////////////////////////////////////////////////
 
 #if SK_SUPPORT_GPU
@@ -620,3 +636,4 @@ void GrGLDisplacementMapEffect::GenKey(const GrProcessor& proc,
     b->add32(xKey | yKey);
 }
 #endif
+