Bug 653990 - preventDefault on touchmove does not completely prevent panning [r=wesj]

mobile/chrome/content/browser.js

@@ -1746,9 +1746,12 @@ const ContentTouchHandler = {
 
         if (json.click)
           this.clickPrevented = true;
+        if (json.panning)
+          this.panningPrevented = true;
 
-        if (this.canCancelPan)
-          Elements.browsers.customDragger.contentMouseCapture = json.panning;
+        // We don't know if panning is allowed until the first touchmove event is processed.
+        if (this.canCancelPan && json.type == "touchmove")
+          Elements.browsers.customDragger.contentMouseCapture = this.panningPrevented;
         break;
       }
       case "Browser:CanCaptureMouse:Return": {
@@ -1790,10 +1793,9 @@ const ContentTouchHandler = {
   },
 
   touchTimeout: null,
-
   canCancelPan: false,
-
   clickPrevented: false,
+  panningPrevented: false,
 
   updateCanCancel: function(aX, aY) {
     let dpi = Browser.windowUtils.displayDPI;
@@ -1823,6 +1825,7 @@ const ContentTouchHandler = {
     // if the page might capture touch events, we give it the option
     this.updateCanCancel(aX, aY);
     this.clickPrevented = false;
+    this.panningPrevented = false;
 
     let dragger = Elements.browsers.customDragger;
     dragger.contentMouseCapture = this.canCancelPan && Browser.selectedTab.contentMightCaptureMouse;

mobile/chrome/content/content.js

@@ -1224,30 +1224,33 @@ var TouchEventHandler = {
       return;
     }
 
-    let cancelled = false;
-
+    let type;
     switch (aMessage.name) {
       case "Browser:MouseDown":
         this.isCancellable = true;
         this.element = elementFromPoint(json.x, json.y);
-        cancelled = !this.sendEvent("touchstart", json, this.element);
+        type = "touchstart";
         break;
 
       case "Browser:MouseUp":
         this.isCancellable = false;
-        if (this.element)
-          this.sendEvent("touchend", json, this.element);
-        this.element = null;
+        type = "touchend";
         break;
 
       case "Browser:MouseMove":
-        if (this.element)
-          cancelled = !this.sendEvent("touchmove", json, this.element);
+        type = "touchmove";
         break;
     }
 
+    if (!this.element)
+      return;
+    let cancelled = !this.sendEvent(type, json, this.element);
+    if (type == "touchend")
+      this.element = null;
+
     if (this.isCancellable) {
       sendAsyncMessage("Browser:CaptureEvents", { messageId: json.messageId,
+                                                  type: type,
                                                   contentMightCaptureMouse: true,
                                                   click: cancelled && aMessage.name == "Browser:MouseDown",
                                                   panning: cancelled });