CtfVisualizer: Allow strings for process and thread id

While the format document only uses numbers for these in its examples,
the data type is not really specified there and chrome://tracing itself
handles strings for them without complaint. On trace-generating side
std::thread::id can't easily be serialized as a number, and strings can
easily be supported in the viewer.

Change-Id: I36c8497049d4933058b9f72a28f24e1d1cf0d5bb
Reviewed-by: Alessandro Portale <alessandro.portale@qt.io>

src/plugins/ctfvisualizer/ctftimelinemodel.h

@@ -28,7 +28,9 @@ class CtfTimelineModel : public Timeline::TimelineModel
 
 public:
     explicit CtfTimelineModel(Timeline::TimelineModelAggregator *parent,
-                              CtfTraceManager *traceManager, int tid, int pid);
+                              CtfTraceManager *traceManager,
+                              const QString &tid,
+                              const QString &pid);
 
     QRgb color(int index) const override;
     QVariantList labels() const override;
@@ -44,7 +46,7 @@ public:
 
     void finalize(double traceBegin, double traceEnd, const QString &processName, const QString &threadName);
 
-    int tid() const;
+    QString tid() const;
     QString eventTitle(int index) const;
 
 signals:
@@ -65,9 +67,9 @@ private:
 protected:
     CtfTraceManager *const m_traceManager;
 
-    int m_threadId;
+    QString m_threadId;
     QString m_threadName;
-    int m_processId;
+    QString m_processId;
     QString m_processName;
 
     int m_maxStackSize = 0;