Bug 1307809 - Add IsOwnedBy() check r=nical

gfx/layers/composite/TextureHost.cpp

@@ -577,9 +577,14 @@ BufferTextureHost::EnsureWrappingTextureSource()
 {
   MOZ_ASSERT(!mHasIntermediateBuffer);
 
-  if (mFirstSource) {
+  if (mFirstSource && mFirstSource->IsOwnedBy(this)) {
     return true;
   }
+  // We don't own it, apparently.
+  if (mFirstSource) {
+    mNeedsFullUpdate = true;
+    mFirstSource = nullptr;
+  }
 
   if (!mCompositor) {
     return false;