Fix flaky parallel recompilation test.

On very rare circumstances parallel recompilation would install
the optimized method earlier than expected and the test would fail.

BUG=
R=yangguo@chromium.org

Review URL: https://codereview.chromium.org/24495005

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@16933 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

test/mjsunit/regress/regress-embedded-cons-string.js

@@ -27,7 +27,7 @@
 
 // Flags: --fold-constants --nodead-code-elimination
 // Flags: --expose-gc --allow-natives-syntax
-// Flags: --concurrent-recompilation --concurrent-recompilation-delay=300
+// Flags: --concurrent-recompilation --concurrent-recompilation-delay=600
 
 if (!%IsConcurrentRecompilationSupported()) {
   print("Concurrent recompilation is disabled. Skipping this test.");