SurfaceFlinger: calculate expected present once

Calculate the expected present time in the beginning of the frame
and use the same value across the frame composition.

Bug: 137873466
Test: App transitions
Change-Id: I0b41c62796f6150702e8d50ec7d28838d3a5aa87
diff --git a/services/surfaceflinger/SurfaceFlinger.h b/services/surfaceflinger/SurfaceFlinger.h
index 556a4b9..d836795 100644
--- a/services/surfaceflinger/SurfaceFlinger.h
+++ b/services/surfaceflinger/SurfaceFlinger.h
@@ -301,10 +301,11 @@
     // TODO: this should be made accessible only to MessageQueue
     void onMessageReceived(int32_t what);
 
-    // Returns the expected present time for this frame.
+    // populates the expected present time for this frame.
     // When we are in negative offsets, we perform a correction so that the
     // predicted vsync for the *next* frame is used instead.
-    nsecs_t getExpectedPresentTime();
+    void populateExpectedPresentTime();
+    nsecs_t getExpectedPresentTime() const { return mExpectedPresentTime; }
 
     // for debugging only
     // TODO: this should be made accessible only to HWComposer
@@ -1184,6 +1185,8 @@
     // Flags to capture the state of Vsync in HWC
     HWC2::Vsync mHWCVsyncState = HWC2::Vsync::Disable;
     HWC2::Vsync mHWCVsyncPendingState = HWC2::Vsync::Disable;
+
+    nsecs_t mExpectedPresentTime;
 };
 
 } // namespace android