Update ColorFilterImageFilter & BlurImageFilter debugger strings

This CL allows us to see the image filter DAG in the debugger.

Review URL: https://codereview.chromium.org/811913004
diff --git a/src/effects/SkColorFilterImageFilter.cpp b/src/effects/SkColorFilterImageFilter.cpp
index 571d69c..acd6fac 100755
--- a/src/effects/SkColorFilterImageFilter.cpp
+++ b/src/effects/SkColorFilterImageFilter.cpp
@@ -146,7 +146,13 @@
 void SkColorFilterImageFilter::toString(SkString* str) const {
     str->appendf("SkColorFilterImageFilter: (");
 
-    str->appendf("color filter: ");
+    str->appendf("input: (");
+
+    if (this->getInput(0)) {
+        this->getInput(0)->toString(str);
+    }
+
+    str->appendf(") color filter: ");
     fColorFilter->toString(str);
 
     str->append(")");