Pass dsl::PositionInfo by value

We were previously using a mix of pass-by-value and pass-by-pointer (to
allow for explicitly null PositionInfo). Being able to pass a null
PositionInfo didn't really add much, since we can just use a nullary-
constructor PositionInfo instead, so these have all been migrated to
by-value.

Change-Id: Ia31e252cac94f64c4b38c29a54e6e7f752e70672
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/437276
Commit-Queue: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
Reviewed-by: John Stiles <johnstiles@google.com>
diff --git a/src/sksl/SkSLCompiler.cpp b/src/sksl/SkSLCompiler.cpp
index 27557c6..90fdf94 100644
--- a/src/sksl/SkSLCompiler.cpp
+++ b/src/sksl/SkSLCompiler.cpp
@@ -986,15 +986,14 @@
 
 #endif // defined(SKSL_STANDALONE) || SK_SUPPORT_GPU
 
-void Compiler::handleError(const char* msg, dsl::PositionInfo* pos) {
+void Compiler::handleError(const char* msg, dsl::PositionInfo pos) {
     if (strstr(msg, POISON_TAG)) {
         // don't report errors on poison values
         return;
     }
     fErrorCount++;
     fErrorTextLength.push_back(fErrorText.length());
-    fErrorText += "error: " + (pos && pos->line() >= 1 ? to_string(pos->line()) + ": " : "") + msg +
-                  "\n";
+    fErrorText += "error: " + (pos.line() >= 1 ? to_string(pos.line()) + ": " : "") + msg + "\n";
 }
 
 void Compiler::setErrorCount(int c) {