extract map copying logic to a separate function

Author: vladima

src/compiler/checker.ts

@@ -3651,9 +3651,7 @@ module ts {
  var maybeCache = maybeStack[depth];
  // If result is definitely true, copy assumptions to global cache, else copy to next level up
  var destinationCache = result === Ternary.True || depth === 0 ? relation : maybeStack[depth - 1];
- for (var p in maybeCache) {
- destinationCache[p] = maybeCache[p];
- }
+ copyMap(maybeCache, destinationCache);
  }
  else {
  // A false result goes straight into global cache (when something is false under assumptions it

src/compiler/core.ts

@@ -208,6 +208,12 @@ module ts {
  return result;
  }
 
+ export function copyMap<T>(source: Map<T>, target: Map<T>): void {
+ for (var p in source) {
+ target[p] = source[p];
+ }
+ }
+
  /**
  * Creates a map from the elements of an array.
  *