DevTools: make profiling lock global rather than per Target

Source/devtools/front_end/sdk/Locks.js

Index: Source/devtools/front_end/sdk/Locks.js
diff --git a/Source/devtools/front_end/sdk/Locks.js b/Source/devtools/front_end/sdk/Locks.js
new file mode 100644
index 0000000000000000000000000000000000000000..b8cea5244e8ea9a0d8ebfab65b89d6f79d410639
--- /dev/null
+++ b/Source/devtools/front_end/sdk/Locks.js
@@ -0,0 +1,13 @@
+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+/**
+ * @return {!WebInspector.Lock}
+ */
+WebInspector.profilingLock = function()
+{
+    if (!WebInspector._profilingLock)
+        WebInspector._profilingLock = new WebInspector.Lock();
+    return WebInspector._profilingLock;
+}