Refactor AnalyzerConfig to use Timestamps instead of microseconds.

Add optional offset-to-UTC parameter to output. This allows aligning
the x-axis in the generated charts to other UTC-based logs.

Bug: b/215140373
Change-Id: I65bcd295718acbb8c94e363907c1abc458067bfd
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/250203
Reviewed-by: Kristoffer Erlandsson <kerl@google.com>
Commit-Queue: Björn Terelius <terelius@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#35992}

rtc_tools/rtc_event_log_visualizer/plot_base.h

@@ -16,6 +16,7 @@
 #include <vector>
 
 #include "absl/base/attributes.h"
+#include "absl/types/optional.h"
 #include "rtc_base/ignore_wundef.h"
 
 RTC_PUSH_IGNORING_WUNDEF()
@@ -194,6 +195,10 @@ class PlotCollection {
 
   virtual Plot* AppendNewPlot();
 
+  void SetCallTimeToUtcOffsetMs(int64_t calltime_to_utc_ms) {
+    calltime_to_utc_ms_ = calltime_to_utc_ms;
+  }
+
   // Replaces PythonPlotCollection::Draw()
   void PrintPythonCode(bool shared_xaxis) const;
 
@@ -202,6 +207,7 @@ class PlotCollection {
 
  protected:
   std::vector<std::unique_ptr<Plot>> plots_;
+  absl::optional<int64_t> calltime_to_utc_ms_;
 };
 
 }  // namespace webrtc