Scrol workspace on mouse wheel and pinch-zoom

Distinguish pinch-zoom in Chrome using e.ctrlKey.

If a mouse wheel event is not a zoom event, scroll the workspace.

#51

core/workspace_svg.js

@@ -668,10 +668,27 @@ Blockly.WorkspaceSvg.prototype.moveDrag = function(e) {
  */
 Blockly.WorkspaceSvg.prototype.onMouseWheel_ = function(e) {
   // TODO: Remove terminateDrag and compensate for coordinate skew during zoom.
-  Blockly.terminateDrag_();
-  var delta = e.deltaY > 0 ? -1 : 1;
-  var position = Blockly.mouseToSvg(e, this.getParentSvg());
-  this.zoom(position.x, position.y, delta);
+  if (e.ctrlKey) {
+    // Pinch-to-zoom in Chrome only
+    Blockly.terminateDrag_();
+    var delta = e.deltaY > 0 ? -1 : 1;
+    var position = Blockly.mouseToSvg(e, this.getParentSvg());
+    this.zoom(position.x, position.y, delta);
+  } else {
+    // This is a regular mouse wheel event - scroll the workspace
+    var metrics = this.getMetrics();
+    var x = this.scrollX - e.deltaX;
+    var y = this.scrollY - e.deltaY;
+    x = Math.min(x, -metrics.contentLeft);
+    y = Math.min(y, -metrics.contentTop);
+    x = Math.max(x, metrics.viewWidth - metrics.contentLeft -
+                 metrics.contentWidth);
+    y = Math.max(y, metrics.viewHeight - metrics.contentTop -
+                 metrics.contentHeight);
+    // Move the scrollbars and the page will scroll automatically.
+    this.scrollbar.set(-x - metrics.contentLeft,
+                       -y - metrics.contentTop);
+  }
   e.preventDefault();
 };