Bug 750243 - Make sure target.currentURI is not null before saving an image r=wesj a=android-only

mobile/android/chrome/content/browser.js

@@ -1140,8 +1140,6 @@ var NativeWindow = {
     _contextId: 0, // id to assign to new context menu items if they are added
 
     init: function() {
-      this.imageContext = this.SelectorContext("img");
-
       Services.obs.addObserver(this, "Gesture:LongPress", false);
 
       // TODO: These should eventually move into more appropriate classes
@@ -1186,18 +1184,17 @@ var NativeWindow = {
                });
 
       this.add(Strings.browser.GetStringFromName("contextmenu.saveImage"),
-               this.imageContext,
+               this.imageSaveableContext,
                function(aTarget) {
                  let imageCache = Cc["@mozilla.org/image/cache;1"].getService(Ci.imgICache);
                  let props = imageCache.findEntryProperties(aTarget.currentURI, aTarget.ownerDocument.characterSet);
-                 var contentDisposition = "";
+                 let contentDisposition = "";
-                 var type = "";
+                 let type = "";
                  try {
                     String(props.get("content-disposition", Ci.nsISupportsCString));
                     String(props.get("type", Ci.nsISupportsCString));
                  } catch(ex) { }
-                 var browser = BrowserApp.getBrowserForDocument(aTarget.ownerDocument);
+                 ContentAreaUtils.internalSave(aTarget.currentURI.spec, null, null, contentDisposition, type, false, "SaveImageTitle", null, aTarget.ownerDocument.documentURIObject, true, null);
-                 ContentAreaUtils.internalSave(aTarget.currentURI.spec, null, null, contentDisposition, type, false, "SaveImageTitle", null, browser.documentURI, true, null);
                });
     },
 
@@ -1285,6 +1282,16 @@ var NativeWindow = {
       }
     },
 
+    imageSaveableContext: {
+      matches: function imageSaveableContextMatches(aElement) {
+        if (aElement instanceof Ci.nsIImageLoadingContent && aElement.currentURI) {
+          // The image must be loaded to allow saving
+          let request = aElement.getRequest(Ci.nsIImageLoadingContent.CURRENT_REQUEST);
+          return (request && (request.imageStatus & request.STATUS_SIZE_AVAILABLE));
+        }
+      }
+    },
+
     _sendToContent: function(aX, aY) {
       // initially we look for nearby clickable elements. If we don't find one we fall back to using whatever this click was on
       let rootElement = ElementTouchHelper.elementFromPoint(BrowserApp.selectedBrowser.contentWindow, aX, aY);