Convert SPIR-V Writer over to utils::StringStream.

This CL updates the spir-v writer to use utils::StringStream.

Bug: tint:1686
Change-Id: I0b1367991de9ecb9fe02bdd0d1827aeba633f2fb
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/121940
Reviewed-by: Ben Clayton <bclayton@google.com>
Commit-Queue: Dan Sinclair <dsinclair@chromium.org>
Kokoro: Kokoro <noreply+kokoro@google.com>
diff --git a/src/tint/writer/spirv/builder.cc b/src/tint/writer/spirv/builder.cc
index ad0d746..40f98d8 100644
--- a/src/tint/writer/spirv/builder.cc
+++ b/src/tint/writer/spirv/builder.cc
@@ -49,6 +49,7 @@
 #include "src/tint/utils/compiler_macros.h"
 #include "src/tint/utils/defer.h"
 #include "src/tint/utils/map.h"
+#include "src/tint/utils/string_stream.h"
 #include "src/tint/writer/append_vector.h"
 #include "src/tint/writer/check_supported_extensions.h"
 
@@ -4138,7 +4139,7 @@
 
 bool Builder::push_function_inst(spv::Op op, const OperandList& operands) {
     if (functions_.empty()) {
-        std::ostringstream ss;
+        utils::StringStream ss;
         ss << "Internal error: trying to add SPIR-V instruction " << int(op)
            << " outside a function";
         error_ = ss.str();