Bug 1874803 - Add sentinel invalid recorded event type. r=gfx-reviewers,lsalzman

RecordedEvent::EventType::INVALID should never be seen in a recording
and so can be used as a sentinel value that we can assert against. If it
is seen, then the recording should fail gracefully.

Differential Revision: https://phabricator.services.mozilla.com/D198649

gfx/2d/InlineTranslator.cpp

@@ -42,7 +42,7 @@ bool InlineTranslator::TranslateRecording(char* aData, size_t aLen) {
     return false;
   }
 
-  uint8_t eventType;
+  uint8_t eventType = RecordedEvent::EventType::INVALID;
   ReadElement(reader, eventType);
   while (reader.good()) {
     bool success = RecordedEvent::DoWithEvent(

gfx/2d/RecordedEvent.h

@@ -367,7 +367,8 @@ class EventStream {
 class RecordedEvent {
  public:
   enum EventType : uint8_t {
-    DRAWTARGETCREATION = 0,
+    INVALID = 0,
+    DRAWTARGETCREATION,
     DRAWTARGETDESTRUCTION,
     SETCURRENTDRAWTARGET,
     FILLRECT,

gfx/layers/ipc/CanvasTranslator.cpp

@@ -538,7 +538,7 @@ void CanvasTranslator::TranslateRecording() {
   });
 
   mHeader->readerState = State::Processing;
-  EventType eventType;
+  EventType eventType = EventType::INVALID;
   while (ReadNextEvent(eventType)) {
     bool success = RecordedEvent::DoWithEventFromReader(
         mCurrentMemReader, eventType,

layout/printing/PrintTranslator.cpp

@@ -48,7 +48,7 @@ bool PrintTranslator::TranslateRecording(PRFileDescStream& aRecording) {
     return false;
   }
 
-  uint8_t eventType;
+  uint8_t eventType = RecordedEvent::EventType::INVALID;
   ReadElement(aRecording, eventType);
   while (aRecording.good()) {
     bool success = RecordedEvent::DoWithEventFromStream(