Add undo checkpoint on drop.

Resolves #188.

build/squire-raw.js

@@ -2228,6 +2228,31 @@ var onPaste = function ( event ) {
     }, 0 );
 };
 
+// On Windows you can drag an drop text. We can't handle this ourselves, because
+// as far as I can see, there's no way to get the drop insertion point. So just
+// save an undo state and hope for the best.
+var onDrop = function ( event ) {
+    var types = event.dataTransfer.types;
+    var l = types.length;
+    var hasPlain = false;
+    var hasHTML = false;
+    while ( l-- ) {
+        switch ( types[l] ) {
+        case 'text/plain':
+            hasPlain = true;
+            break;
+        case 'text/html':
+            hasHTML = true;
+            break;
+        default:
+            return;
+        }
+    }
+    if ( hasHTML || hasPlain ) {
+        this.saveUndoState();
+    }
+};
+
 var instances = [];
 
 function getSquireInstance ( doc ) {
@@ -2328,6 +2353,7 @@ function Squire ( root, config ) {
     this.addEventListener( isIElt11 ? 'beforecut' : 'cut', onCut );
     this.addEventListener( 'copy', onCopy );
     this.addEventListener( isIElt11 ? 'beforepaste' : 'paste', onPaste );
+    this.addEventListener( 'drop', onDrop );
 
     // Opera does not fire keydown repeatedly.
     this.addEventListener( isPresto ? 'keypress' : 'keydown', onKey );

source/Clipboard.js

@@ -206,3 +206,28 @@ var onPaste = function ( event ) {
         }
     }, 0 );
 };
+
+// On Windows you can drag an drop text. We can't handle this ourselves, because
+// as far as I can see, there's no way to get the drop insertion point. So just
+// save an undo state and hope for the best.
+var onDrop = function ( event ) {
+    var types = event.dataTransfer.types;
+    var l = types.length;
+    var hasPlain = false;
+    var hasHTML = false;
+    while ( l-- ) {
+        switch ( types[l] ) {
+        case 'text/plain':
+            hasPlain = true;
+            break;
+        case 'text/html':
+            hasHTML = true;
+            break;
+        default:
+            return;
+        }
+    }
+    if ( hasHTML || hasPlain ) {
+        this.saveUndoState();
+    }
+};

source/Editor.js

@@ -100,6 +100,7 @@ function Squire ( root, config ) {
     this.addEventListener( isIElt11 ? 'beforecut' : 'cut', onCut );
     this.addEventListener( 'copy', onCopy );
     this.addEventListener( isIElt11 ? 'beforepaste' : 'paste', onPaste );
+    this.addEventListener( 'drop', onDrop );
 
     // Opera does not fire keydown repeatedly.
     this.addEventListener( isPresto ? 'keypress' : 'keydown', onKey );