Moved JsonPrefStore to use SequencedWorkerPool

chrome/browser/profiles/profile_impl.cc

Index: chrome/browser/profiles/profile_impl.cc
diff --git a/chrome/browser/profiles/profile_impl.cc b/chrome/browser/profiles/profile_impl.cc
index 98cd169196aabbd48c1a770d63a16a5441d6c810..fa94dd8edf8cd9ef3c61189ea7ff4ad9d7fc5359 100644
--- a/chrome/browser/profiles/profile_impl.cc
+++ b/chrome/browser/profiles/profile_impl.cc
@@ -16,6 +16,7 @@
 #include "base/string_tokenizer.h"
 #include "base/string_util.h"
 #include "base/stringprintf.h"
+#include "base/threading/sequenced_worker_pool.h"
 #include "base/utf_string_conversions.h"
 #include "base/version.h"
 #include "chrome/browser/autocomplete/autocomplete_classifier.h"
@@ -210,10 +211,17 @@ Profile* Profile::CreateProfile(const FilePath& path,
                                 CreateMode create_mode) {
   if (create_mode == CREATE_MODE_ASYNCHRONOUS) {
     DCHECK(delegate);
-    // This is safe while all file operations are done on the FILE thread.
-    BrowserThread::PostTask(
-        BrowserThread::FILE, FROM_HERE,
-        base::Bind(&CreateDirectoryNoResult, path));
+    // We need to make sure that profile directory is created on the same
+    // blocking pool where we will run all its important file serialization
+    // tasks (i.e. JsonPrefStore).
+    scoped_refptr<base::SequencedTaskRunner> task_runner =
+        BrowserThread::GetBlockingPool()->
+          GetSequencedTaskRunnerWithShutdownBehavior(
+              BrowserThread::GetBlockingPool()->GetNamedSequenceToken(
+                  path.AsUTF8Unsafe()),

[willchan no longer on Chromium, 2012/10/11 23:19:31]

The only thing that makes me feel nervous about this is the lack of enforcement
that the different requests all use this token. Where's the JsonPrefStore
created? Can we pass this specific SequencedTaskRunner to it somehow to enforce
that even if this token changes, they both end up using the same token?
Otherwise it feels a bit fragile.

[zel, 2012/10/12 23:15:32]

I have isolated SequencedTaskRunner and shared it for profile creation, this
unfortunately introduces two factory methods for JSonPrefStore again... PTAL

+              base::SequencedWorkerPool::BLOCK_SHUTDOWN);
+    task_runner->PostTask(FROM_HERE,
+                          base::Bind(&CreateDirectoryNoResult, path));
   } else if (create_mode == CREATE_MODE_SYNCHRONOUS) {
     if (!file_util::PathExists(path)) {
       // TODO(tc): http://b/1094718 Bad things happen if we can't write to the