DevTools: make profiling lock global rather than per Target

Source/devtools/front_end/common/Lock.js

Index: Source/devtools/front_end/common/Lock.js
diff --git a/Source/devtools/front_end/common/Lock.js b/Source/devtools/front_end/common/Lock.js
new file mode 100644
index 0000000000000000000000000000000000000000..a33e54be4cbfd103ff27746fc7847ece2835d997
--- /dev/null
+++ b/Source/devtools/front_end/common/Lock.js
@@ -0,0 +1,48 @@
+// 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.
+
+/**
+ * @constructor
+ * @extends {WebInspector.Object}
+ */
+WebInspector.Lock = function()
+{
+    this._count = 0; // Reentrant.
+}
+
+/**
+ * @enum {string}
+ */
+WebInspector.Lock.Events = {
+    StateChanged: "StateChanged"
+}
+
+WebInspector.Lock.prototype = {
+    /**
+     * @return {boolean}
+     */
+    isAcquired: function()
+    {
+        return !!this._count;
+    },
+
+    acquire: function()
+    {
+        if (++this._count === 1)
+            this.dispatchEventToListeners(WebInspector.Lock.Events.StateChanged);
+    },
+
+    release: function()
+    {
+        --this._count;
+        if (this._count < 0) {
+            console.error("WebInspector.Lock acquire/release calls are unbalanced " + new Error().stack);
+            return;
+        }
+        if (!this._count)
+            this.dispatchEventToListeners(WebInspector.Lock.Events.StateChanged);
+    },
+
+    __proto__: WebInspector.Object.prototype
+}