Bug 936380 - Fix gcli screenshot size calculations. r=jwalker

toolkit/devtools/gcli/commands/screenshot.js

@@ -109,30 +109,36 @@ exports.items = [
         let currentX = window.scrollX;
         let currentY = window.scrollY;
 
-        if (!fullpage) {
-          if (!node) {
-            left = window.scrollX;
-            top = window.scrollY;
-            width = window.innerWidth;
-            height = window.innerHeight;
-          } else {
-            let lh = new LayoutHelpers(window);
-            let rect = lh.getRect(node, window);
-            top = rect.top;
-            left = rect.left;
-            width = rect.width;
-            height = rect.height;
-          }
-        } else {
-          // Bug 961832: GCLI screenshot shows fixed position element in wrong position if
-          // we don't scroll to top
+        if (fullpage) {
+          // Bug 961832: GCLI screenshot shows fixed position element in wrong
+          // position if we don't scroll to top
           window.scrollTo(0,0);
           width = window.innerWidth + window.scrollMaxX;
           height = window.innerHeight + window.scrollMaxY;
+        } else if (node) {
+          let lh = new LayoutHelpers(window);
+          let rect = lh.getRect(node, window);
+          top = rect.top;
+          left = rect.left;
+          width = rect.width;
+          height = rect.height;
+        } else {
+          left = window.scrollX;
+          top = window.scrollY;
+          width = window.innerWidth;
+          height = window.innerHeight;
         }
+
+        let winUtils = window.QueryInterface(Ci.nsIInterfaceRequestor)
+                             .getInterface(Ci.nsIDOMWindowUtils);
+        let scrollbarHeight = {};
+        let scrollbarWidth = {};
+        winUtils.getScrollbarSize(false, scrollbarWidth, scrollbarHeight);
+        width -= scrollbarWidth.value;
+        height -= scrollbarHeight.value;
+
         canvas.width = width;
         canvas.height = height;
-
         let ctx = canvas.getContext("2d");
         ctx.drawWindow(window, left, top, width, height, "#fff");
         let data = canvas.toDataURL("image/png", "");