Ensure that content will consistently return the same MessageLoopProxy for a given BrowserThread

BUG=378079
R=jam@chromium.org

Review URL: https://codereview.chromium.org/314053003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@276334 0039d316-1c4b-4281-b951-d872f2087c98

content/browser/browser_thread_impl.cc

@@ -31,6 +31,57 @@ static const char* g_browser_thread_names[BrowserThread::ID_COUNT] = {
   "Chrome_IOThread",  // IO
 };
 
+// An implementation of MessageLoopProxy to be used in conjunction
+// with BrowserThread.
+class BrowserThreadMessageLoopProxy : public base::MessageLoopProxy {
+ public:
+  explicit BrowserThreadMessageLoopProxy(BrowserThread::ID identifier)
+      : id_(identifier) {
+  }
+
+  // MessageLoopProxy implementation.
+  virtual bool PostDelayedTask(
+      const tracked_objects::Location& from_here,
+      const base::Closure& task, base::TimeDelta delay) OVERRIDE {
+    return BrowserThread::PostDelayedTask(id_, from_here, task, delay);
+  }
+
+  virtual bool PostNonNestableDelayedTask(
+      const tracked_objects::Location& from_here,
+      const base::Closure& task,
+      base::TimeDelta delay) OVERRIDE {
+    return BrowserThread::PostNonNestableDelayedTask(id_, from_here, task,
+                                                     delay);
+  }
+
+  virtual bool RunsTasksOnCurrentThread() const OVERRIDE {
+    return BrowserThread::CurrentlyOn(id_);
+  }
+
+ protected:
+  virtual ~BrowserThreadMessageLoopProxy() {}
+
+ private:
+  BrowserThread::ID id_;
+  DISALLOW_COPY_AND_ASSIGN(BrowserThreadMessageLoopProxy);
+};
+
+// A separate helper is used just for the proxies, in order to avoid needing
+// to initialize the globals to create a proxy.
+struct BrowserThreadProxies {
+  BrowserThreadProxies() {
+    for (int i = 0; i < BrowserThread::ID_COUNT; ++i) {
+      proxies[i] =
+          new BrowserThreadMessageLoopProxy(static_cast<BrowserThread::ID>(i));
+    }
+  }
+
+  scoped_refptr<base::MessageLoopProxy> proxies[BrowserThread::ID_COUNT];
+};
+
+base::LazyInstance<BrowserThreadProxies>::Leaky
+    g_proxies = LAZY_INSTANCE_INITIALIZER;
+
 struct BrowserThreadGlobals {
   BrowserThreadGlobals()
       : blocking_pool(new base::SequencedWorkerPool(3, "BrowserBlocking")) {
@@ -274,41 +325,6 @@ bool BrowserThreadImpl::PostTaskHelper(
   return !!message_loop;
 }
 
-// An implementation of MessageLoopProxy to be used in conjunction
-// with BrowserThread.
-class BrowserThreadMessageLoopProxy : public base::MessageLoopProxy {
- public:
-  explicit BrowserThreadMessageLoopProxy(BrowserThread::ID identifier)
-      : id_(identifier) {
-  }
-
-  // MessageLoopProxy implementation.
-  virtual bool PostDelayedTask(
-      const tracked_objects::Location& from_here,
-      const base::Closure& task, base::TimeDelta delay) OVERRIDE {
-    return BrowserThread::PostDelayedTask(id_, from_here, task, delay);
-  }
-
-  virtual bool PostNonNestableDelayedTask(
-      const tracked_objects::Location& from_here,
-      const base::Closure& task,
-      base::TimeDelta delay) OVERRIDE {
-    return BrowserThread::PostNonNestableDelayedTask(id_, from_here, task,
-                                                     delay);
-  }
-
-  virtual bool RunsTasksOnCurrentThread() const OVERRIDE {
-    return BrowserThread::CurrentlyOn(id_);
-  }
-
- protected:
-  virtual ~BrowserThreadMessageLoopProxy() {}
-
- private:
-  BrowserThread::ID id_;
-  DISALLOW_COPY_AND_ASSIGN(BrowserThreadMessageLoopProxy);
-};
-
 // static
 bool BrowserThread::PostBlockingPoolTask(
     const tracked_objects::Location& from_here,
@@ -477,7 +493,7 @@ bool BrowserThread::GetCurrentThreadIdentifier(ID* identifier) {
 // static
 scoped_refptr<base::MessageLoopProxy>
 BrowserThread::GetMessageLoopProxyForThread(ID identifier) {
-  return make_scoped_refptr(new BrowserThreadMessageLoopProxy(identifier));
+  return g_proxies.Get().proxies[identifier];
 }
 
 // static