Fix typo in chrome://flags/#enable-parallel-downloading

Bug: 
Change-Id: Iddc38fc951d51d1c2f1d7f59132ffae9cd209dbc
Reviewed-on: https://chromium-review.googlesource.com/779100Reviewed-by: Alex Moshchuk <alexmos@chromium.org>
Commit-Queue: Alex Moshchuk <alexmos@chromium.org>
Cr-Commit-Position: refs/heads/master@{#517871}

chrome/browser/flag_descriptions.cc

@@ -1029,8 +1029,7 @@ const char kOverscrollStartThreshold200Percent[] = "200%";
 
 const char kParallelDownloadingName[] = "Parallel downloading";
 const char kParallelDownloadingDescription[] =
-    "Enable parallel downloading to"
-    "accelerate download speed.";
+    "Enable parallel downloading to accelerate download speed.";
 
 const char kPassiveEventListenerDefaultName[] =
     "Passive Event Listener Override";