Fix truncation of frame time on 32-bit Android. (#4040)

shell/common/animator.cc

@@ -62,9 +62,7 @@ void Animator::BeginFrame(ftl::TimePoint frame_time) {
   // to service potential frame.
   FTL_DCHECK(producer_continuation_);
 
-  // TODO(abarth): We should use |frame_time| instead, but the frame time we get
-  // on Android appears to be unstable.
-  last_begin_frame_time_ = ftl::TimePoint::Now();
+  last_begin_frame_time_ = frame_time;
   engine_->BeginFrame(last_begin_frame_time_);
 }
 

shell/platform/android/vsync_waiter_android.cc

@@ -37,7 +37,7 @@ void VsyncWaiterAndroid::AsyncWaitForVsync(Callback callback) {
   });
 }
 
-void VsyncWaiterAndroid::OnVsync(long frameTimeNanos) {
+void VsyncWaiterAndroid::OnVsync(int64_t frameTimeNanos) {
   Callback callback = std::move(callback_);
   callback_ = Callback();
   blink::Threads::UI()->PostTask([callback, frameTimeNanos] {
@@ -61,7 +61,7 @@ static void OnNativeVsync(JNIEnv* env,
   VsyncWaiterAndroid* waiter = weak->get();
   delete weak;
   if (waiter) {
-    waiter->OnVsync(frameTimeNanos);
+    waiter->OnVsync(static_cast<int64_t>(frameTimeNanos));
   }
 }
 

shell/platform/android/vsync_waiter_android.h

@@ -22,7 +22,7 @@ class VsyncWaiterAndroid : public VsyncWaiter {
 
   void AsyncWaitForVsync(Callback callback) override;
 
-  void OnVsync(long frameTimeNanos);
+  void OnVsync(int64_t frameTimeNanos);
 
  private:
   Callback callback_;