Bug 1645540: Make IpdlQueue resize buffers when initial deserialization estimate was low r=jgilbert

When inserting an argument into the IpdlQueue for transmission, we need to resize the internal buffer if we end up with more data than expected.

Differential Revision: https://phabricator.services.mozilla.com/D79581

dom/canvas/IpdlQueue.h

@@ -423,7 +423,11 @@ class IpdlProducer final : public SupportsWeakPtr<IpdlProducer<_Actor>> {
   template <typename Arg>
   QueueStatus WriteObject(size_t aRead, size_t* aWrite, const Arg& arg,
                           size_t aArgSize) {
-    // TODO: Queue needs one extra byte for PCQ (fixme).
+    if (mSerializedData.Length() < (*aWrite) + aArgSize) {
+      // Previous MinSizeOfArgs estimate was insufficient.  Resize the
+      // buffer to accomodate our real needs.
+      mSerializedData.SetLength(*aWrite + aArgSize);
+    }
     return mozilla::webgl::Marshaller::WriteObject(
         mSerializedData.Elements(), mSerializedData.Length() + 1, aRead, aWrite,
         arg, aArgSize);