Replace ModulateRGBA effect with Xfermode using modulate blend.

This reduces our code size by reusing existing components to perform
the same blend, and generates a shader that should be conceptually
equivalent (although it gives the inliner a bit more work to do).

Change-Id: Ie2203f7613503476fa9d045aba58d9ef39f3ea26
Bug: skia:10457
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/302264
Commit-Queue: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
diff --git a/src/gpu/GrProcessorUnitTest.cpp b/src/gpu/GrProcessorUnitTest.cpp
index 7b8cd20..d257e44 100644
--- a/src/gpu/GrProcessorUnitTest.cpp
+++ b/src/gpu/GrProcessorUnitTest.cpp
@@ -81,7 +81,7 @@
  * we verify the count is as expected.  If a new factory is added, then these numbers must be
  * manually adjusted.
  */
-static const int kFPFactoryCount = 38;
+static const int kFPFactoryCount = 37;
 static const int kGPFactoryCount = 14;
 static const int kXPFactoryCount = 4;