Revert "switched skslc from std::string to SkString"

This reverts commit d8df21a1e08b5b3380261f4b90acfbdc538ef93c.

Reason for revert: Breaking Roll

Original change's description:
> 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>
> 

TBR=bsalomon@google.com,benjaminwagner@google.com,ethannicholas@google.com,reviews@skia.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Change-Id: I84d5311beb9d5e607b7a4a3c138332f0c8f19648
Reviewed-on: https://skia-review.googlesource.com/5077
Commit-Queue: Greg Daniel <egdaniel@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>
diff --git a/src/sksl/ast/SkSLASTFunction.h b/src/sksl/ast/SkSLASTFunction.h
index 32f4da7..c5c3b9a 100644
--- a/src/sksl/ast/SkSLASTFunction.h
+++ b/src/sksl/ast/SkSLASTFunction.h
@@ -19,7 +19,7 @@
  * A function declaration or definition. The fBody field will be null for declarations. 
  */
 struct ASTFunction : public ASTDeclaration {
-    ASTFunction(Position position, std::unique_ptr<ASTType> returnType, SkString name,
+    ASTFunction(Position position, std::unique_ptr<ASTType> returnType, std::string name,
                 std::vector<std::unique_ptr<ASTParameter>> parameters, 
                 std::unique_ptr<ASTBlock> body)
     : INHERITED(position, kFunction_Kind)
@@ -28,8 +28,8 @@
     , fParameters(std::move(parameters))
     , fBody(std::move(body)) {}
 
-    SkString description() const override {
-        SkString result = fReturnType->description() + " " + fName + "(";
+    std::string description() const override {
+        std::string result = fReturnType->description() + " " + fName + "(";
         for (size_t i = 0; i < fParameters.size(); i++) {
             if (i > 0) {
                 result += ", ";
@@ -45,7 +45,7 @@
     }
 
     const std::unique_ptr<ASTType> fReturnType;
-    const SkString fName;
+    const std::string fName;
     const std::vector<std::unique_ptr<ASTParameter>> fParameters;
     const std::unique_ptr<ASTBlock> fBody;