8004170: G1: Verbose GC output is not getting flushed to log file using JDK 8

Summary: Add flushes to G1CollectedHeap::log_gc_footer() and TraceCPUTime destructor.
Reviewed-by: jwilhelm, azeemj, brutisso

src/share/vm/gc_implementation/g1/g1CollectedHeap.cpp

@@ -3690,6 +3690,7 @@ void G1CollectedHeap::log_gc_footer(double pause_time_sec) {
     g1_policy()->print_heap_transition();
     gclog_or_tty->print_cr(", %3.7f secs]", pause_time_sec);
   }
+  gclog_or_tty->flush();
 }
 
 bool
@@ -4036,9 +4037,10 @@ G1CollectedHeap::do_collection_pause_at_safepoint(double target_pause_time_ms) {
 #endif
 
       gc_epilogue(false);
+    }
 
+    // Print the remainder of the GC log output.
     log_gc_footer(os::elapsedTime() - pause_start_sec);
-    }
 
     // It is not yet to safe to tell the concurrent mark to
     // start as we have some optional output below. We don't want the

src/share/vm/runtime/timer.cpp

@@ -213,5 +213,6 @@ TraceCPUTime::~TraceCPUTime() {
     if (_print_cr) {
       _logfile->print_cr("");
     }
+    _logfile->flush();
   }
 }