Speed up single-line deltas

2e6f12725b slowed down the application of
deltas that only affect a single line. The slow-down, though trivial for
a single line, is significant for operations than separately modify
thousands of rows (such as indenting a large document).

This commit speeds up single-line deltas by avoiding unnecessary calls
to splitLine() and joinLineWithNext().

lib/ace/document.js

@@ -261,9 +261,13 @@ var Document = function(textOrLines) {
             throw errorText;
         }
         
+        // Validate action.
+        if (delta.action != 'insert' && delta.action != 'delete')
+            fnThrow('Delta action must be "insert" or "delete".');
+        
         // Validate lines.
         if (!delta.lines instanceof Array)
-            fnThrow('Delta object lines must be an array');
+            fnThrow('Delta lines must be an array');
         
         // Validate range type.
         if (!delta.range instanceof Range)
@@ -567,8 +571,30 @@ var Document = function(textOrLines) {
         this.$validateDelta(delta);
         
         // Apply delta.
-        switch (delta.action)
+        if (delta.range.start.row == delta.range.end.row)
         {
+            // Apply single-line delta.
+            // Note: The multi-line code below correctly handle single-line
+            //       deltas too, but we need to short-circuit for speed.
+            var row         = delta.range.start.row;
+            var startColumn = delta.range.start.column;
+            var endColumn   = delta.range.end.column;
+            var line        = this.$lines[row];
+            switch (delta.action) {
+                
+                case 'insert':
+                    this.$lines[row] = line.substring(0, startColumn) + delta.lines[0] + line.substring(startColumn);
+                    break;
+                
+                case 'delete':
+                    this.$lines[row] = line.substring(0, startColumn) + line.substring(endColumn);
+                    break;
+            }
+        } else {
+            
+            // Apply multi-line delta.
+            switch (delta.action) {
+                
                 case 'insert':
                     splitLine(this.$lines, delta.range.start);
                     for (var i = 0; i < delta.lines.length; i++) {
@@ -588,9 +614,7 @@ var Document = function(textOrLines) {
                     );
                     joinLineWithNext(this.$lines, delta.range.start.row);
                     break;
-            
+            }
-            default:
-                throw 'Invalid delta type: ' + delta.action
         }
         
         this._emit("change", { data: delta });