Bug 1482795 - Fix the gfx memory pressure observer. r=sotaro

gfx/layers/MemoryPressureObserver.cpp

@@ -56,7 +56,7 @@ MemoryPressureObserver::Observe(nsISupports* aSubject,
                                 const char* aTopic,
                                 const char16_t* aData)
 {
-  if (mListener && strcmp(aTopic, "memory-pressure")) {
+  if (mListener && strcmp(aTopic, "memory-pressure") == 0) {
     MemoryPressureReason reason = MemoryPressureReason::LOW_MEMORY;
     auto reason_string = nsDependentString(aData);
     if (StringBeginsWith(reason_string, NS_LITERAL_STRING("low-memory-ongoing"))) {

widget/PuppetWidget.cpp

@@ -1137,7 +1137,7 @@ void
 PuppetWidget::OnMemoryPressure(layers::MemoryPressureReason aWhy)
 {
   if (aWhy != MemoryPressureReason::LOW_MEMORY_ONGOING &&
-      mVisible &&
+      !mVisible &&
       mLayerManager &&
       XRE_IsContentProcess()) {
     mLayerManager->ClearCachedResources();