Bug 1839396 part 1 - Explicit Sprinter::forwardOutOfMemory(). r=mgaudet

This change move the error reporting to the JSContext to be an independent
function, such that we can later migrate `Sprinter::put` to become infallible.

Differential Revision: https://phabricator.services.mozilla.com/D181486

js/public/Printer.h

@@ -134,6 +134,13 @@ class JS_PUBLIC_API Sprinter final : public GenericPrinter {
   // first call to this function calls JS_ReportOutOfMemory, and sets this
   // Sprinter's outOfMemory flag; subsequent calls do nothing.
   virtual void reportOutOfMemory() override;
+
+  // When an OOM has already been reported on the Sprinter, this function will
+  // forward this error to the JSContext given in the Sprinter initialization.
+  //
+  // If no JSContext had been provided or the Sprinter is configured to not
+  // report OOM, then nothing happens.
+  void forwardOutOfMemory();
 };
 
 // Fprinter, print a string directly into a file.

js/src/vm/Printer.cpp

@@ -223,10 +223,15 @@ void Sprinter::reportOutOfMemory() {
   if (hadOOM_) {
     return;
   }
+  hadOOM_ = true;
+  forwardOutOfMemory();
+}
+
+void Sprinter::forwardOutOfMemory() {
+  MOZ_ASSERT(hadOOM_);
   if (maybeCx && shouldReportOOM) {
     ReportOutOfMemory(maybeCx);
   }
-  hadOOM_ = true;
 }
 
 bool Sprinter::jsprintf(const char* format, ...) {