switched skslc from std::string to SkString

BUG=skia:

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=4977

Change-Id: I15e24963b09b719a2c07da67745114f5ac66cee8
Reviewed-on: https://skia-review.googlesource.com/4977
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
diff --git a/src/sksl/ast/SkSLASTCallSuffix.h b/src/sksl/ast/SkSLASTCallSuffix.h
index 5cff6f6..356ac85 100644
--- a/src/sksl/ast/SkSLASTCallSuffix.h
+++ b/src/sksl/ast/SkSLASTCallSuffix.h
@@ -8,7 +8,6 @@
 #ifndef SKSL_ASTCALLSUFFIX
 #define SKSL_ASTCALLSUFFIX
 
-#include <sstream>
 #include <vector>
 #include "SkSLASTSuffix.h"
 
@@ -22,9 +21,9 @@
     : INHERITED(position, ASTSuffix::kCall_Kind)
     , fArguments(std::move(arguments)) {}
 
-    std::string description() const override {
-        std::string result("(");
-        std::string separator = "";
+    SkString description() const override {
+        SkString result("(");
+        SkString separator;
         for (size_t i = 0; i < fArguments.size(); ++i) {
             result += separator;
             separator = ", ";