[SurfaceFlinger] Add vsync offset information to systrace.

* Trace offset values in DispSyncSource
* Trace offset type in VSyncModulator
* Refactor how offsets are stored so that refresh rate type can be
encoded in VSyncModulator
* Add locking to catch a potential race condition when updating offsets,
as phase offsets can be accessed or updated on multiple threads.

Bug: 133325345
Test: verified that correct offsets are reported in systrace
Change-Id: I38d43b722cd54728a2e4de3df7dd472aceb1de15
diff --git a/services/surfaceflinger/Scheduler/DispSyncSource.h b/services/surfaceflinger/Scheduler/DispSyncSource.h
index b6785c5..50560a5 100644
--- a/services/surfaceflinger/Scheduler/DispSyncSource.h
+++ b/services/surfaceflinger/Scheduler/DispSyncSource.h
@@ -39,12 +39,16 @@
     // The following method is the implementation of the DispSync::Callback.
     virtual void onDispSyncEvent(nsecs_t when);
 
+    void tracePhaseOffset() REQUIRES(mVsyncMutex);
+
     const char* const mName;
     int mValue = 0;
 
     const bool mTraceVsync;
     const std::string mVsyncOnLabel;
     const std::string mVsyncEventLabel;
+    const std::string mVsyncOffsetLabel;
+    const std::string mVsyncNegativeOffsetLabel;
     nsecs_t mLastCallbackTime GUARDED_BY(mVsyncMutex) = 0;
 
     DispSync* mDispSync;
@@ -58,4 +62,4 @@
     bool mEnabled GUARDED_BY(mVsyncMutex) = false;
 };
 
-} // namespace android
\ No newline at end of file
+} // namespace android