[gtk/wip/alexl/broadway5: 7/13] broadway: Refcount textures

[Alexander Larsson <alexl src gnome org>]

commit 59ddba67568a5338370443f2607d597ba8644cd4
Author: Alexander Larsson <alexl redhat com>
Date:   Fri Mar 22 16:41:19 2019 +0100

    broadway: Refcount textures
    
    We want to delay some rendering, and to make that safe we need to correctly
    refcount the use of blob uris for the textures so that we don't unref
    it while something is scheduled to use it.

 gdk/broadway/broadway.js | 36 ++++++++++++++++++++++++++++--------
 1 file changed, 28 insertions(+), 8 deletions(-)
---
diff --git a/gdk/broadway/broadway.js b/gdk/broadway/broadway.js
index 86259aa0a5..e246948e11 100644
--- a/gdk/broadway/broadway.js
+++ b/gdk/broadway/broadway.js
@@ -128,6 +128,27 @@ function getButtonMask (button) {
     return 0;
 }
 
+function Texture(id, data) {
+    var blob = new Blob([data],{type: "image/png"});
+    this.url = window.URL.createObjectURL(blob);
+    this.refcount = 1;
+    this.id = id;
+    textures[id] = this;
+}
+
+Texture.prototype.ref = function() {
+    this.refcount += 1;
+    return this;
+}
+
+Texture.prototype.unref = function() {
+    this.refcount -= 1;
+    if (this.refcount == 0) {
+        window.URL.revokeObjectURL(this.url);
+        delete textures[this.id];
+    }
+}
+
 function sendConfigureNotify(surface)
 {
     sendInput("w", [surface.id, surface.x, surface.y, surface.width, surface.height]);
@@ -499,8 +520,11 @@ SwapNodes.prototype.insertNode = function(parent, posInParent, oldNode)
             image.height = rect.height;
             image.style["position"] = "absolute";
             set_rect_style(image, rect);
-            var texture_url = textures[texture_id];
-            image.src = texture_url;
+            var texture = textures[texture_id];
+            image.src = texture.url;
+            texture.ref();
+            // Unref blob url when loaded
+            image.onload = function() { texture.unref(); };
             newNode = image;
         }
         break;
@@ -789,16 +813,12 @@ function cmdSurfaceSetNodes(id, node_data)
 
 function cmdUploadTexture(id, data)
 {
-    var blob = new Blob([data],{type: "image/png"});
-    var url = window.URL.createObjectURL(blob);
-    textures[id] = url;
+    new Texture (id, data); // Stores a ref in textures
 }
 
 function cmdReleaseTexture(id)
 {
-    var url = textures[id];
-    window.URL.revokeObjectURL(url);
-    delete textures[id];
+    textures[id].unref();
 }
 
 function cmdGrabPointer(id, ownerEvents)