DevTools: Support async call stacks for FileSystem API (part 1).

Source/modules/filesystem/DOMFileSystem.h

Index: Source/modules/filesystem/DOMFileSystem.h
diff --git a/Source/modules/filesystem/DOMFileSystem.h b/Source/modules/filesystem/DOMFileSystem.h
index 9a1ae67cc40b9890bf17d5637ead428b1b37ba90..ae07a04c4a016e6e1bd1c62c000bb10a835121d9 100644
--- a/Source/modules/filesystem/DOMFileSystem.h
+++ b/Source/modules/filesystem/DOMFileSystem.h
@@ -105,9 +105,25 @@ public:
 private:
     DOMFileSystem(ExecutionContext*, const String& name, FileSystemType, const KURL& rootURL);
 
+    class DispatchCallbackTaskBase : public ExecutionContextTask {
+    public:
+        DispatchCallbackTaskBase()
+            : m_taskName("FileSystem")
+        {
+        }
+
+        virtual const String& taskNameForInstrumentation() const OVERRIDE

[yurys, 2014/07/14 14:55:54]

Why do we return constr String& rather than String from this method in
ExecutionContextTask?

+        {
+            return m_taskName;
+        }
+
+    private:
+        const String m_taskName;
+    };
+
     // A helper template to schedule a callback task.
     template <typename CB, typename CBArg>
-    class DispatchCallbackRefPtrArgTask FINAL : public ExecutionContextTask {
+    class DispatchCallbackRefPtrArgTask FINAL : public DispatchCallbackTaskBase {
     public:
         DispatchCallbackRefPtrArgTask(PassOwnPtr<CB> callback, PassRefPtrWillBeRawPtr<CBArg> arg)
             : m_callback(callback)
@@ -126,7 +142,7 @@ private:
     };
 
     template <typename CB, typename CBArg>
-    class DispatchCallbackPtrArgTask FINAL : public ExecutionContextTask {
+    class DispatchCallbackPtrArgTask FINAL : public DispatchCallbackTaskBase {
     public:
         DispatchCallbackPtrArgTask(PassOwnPtr<CB> callback, CBArg* arg)
             : m_callback(callback)
@@ -145,7 +161,7 @@ private:
     };
 
     template <typename CB, typename CBArg>
-    class DispatchCallbackNonPtrArgTask FINAL : public ExecutionContextTask {
+    class DispatchCallbackNonPtrArgTask FINAL : public DispatchCallbackTaskBase {
     public:
         DispatchCallbackNonPtrArgTask(PassOwnPtr<CB> callback, const CBArg& arg)
             : m_callback(callback)
@@ -164,7 +180,7 @@ private:
     };
 
     template <typename CB>
-    class DispatchCallbackNoArgTask FINAL : public ExecutionContextTask {
+    class DispatchCallbackNoArgTask FINAL : public DispatchCallbackTaskBase {
     public:
         DispatchCallbackNoArgTask(PassOwnPtr<CB> callback)
             : m_callback(callback)