Add `GrProcessor::onDumpInfo` for subclass info dumps.

This CL also marks `GrProcessor::dumpInfo` as final. This prevents a
subclass from mistakenly overriding `dumpInfo` instead of `onDumpInfo`.

`onDumpInfo` is responsible for providing the same data as `dumpInfo`,
except that the FP name is automatically prepended.

Change-Id: I2b44c30a01bc65e9d88321cc21651a94e20074c6
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/309793
Commit-Queue: John Stiles <johnstiles@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
diff --git a/src/gpu/effects/generated/GrMixerEffect.cpp b/src/gpu/effects/generated/GrMixerEffect.cpp
index eadb2f3..ab98376 100644
--- a/src/gpu/effects/generated/GrMixerEffect.cpp
+++ b/src/gpu/effects/generated/GrMixerEffect.cpp
@@ -70,7 +70,5 @@
     return std::make_unique<GrMixerEffect>(*this);
 }
 #if GR_TEST_UTILS
-SkString GrMixerEffect::dumpInfo() const {
-    return SkStringPrintf("MixerEffect(weight=%f)", weight);
-}
+SkString GrMixerEffect::onDumpInfo() const { return SkStringPrintf("(weight=%f)", weight); }
 #endif