Update GrSwizzle to only store key and not string.

Change-Id: Ieaba188e620e5c1f1d423109e628b0ca78f3afe0
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/257394
Reviewed-by: Brian Salomon <bsalomon@google.com>
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
Commit-Queue: Greg Daniel <egdaniel@google.com>
diff --git a/src/gpu/GrFragmentProcessor.cpp b/src/gpu/GrFragmentProcessor.cpp
index 5299c07..b836be4 100644
--- a/src/gpu/GrFragmentProcessor.cpp
+++ b/src/gpu/GrFragmentProcessor.cpp
@@ -169,7 +169,7 @@
                     GrGLSLFPFragmentBuilder* fragBuilder = args.fFragBuilder;
 
                     fragBuilder->codeAppendf("%s = %s.%s;",
-                                             args.fOutputColor, args.fInputColor, swizzle.c_str());
+                            args.fOutputColor, args.fInputColor, swizzle.asString().c_str());
                 }
             };
             return new GLFP;