Oilpan: A precise GC should be prioritized than an idle GC

For now, this CL doesn't change any behavior since there is no opportunity
where precise GCs and idle GCs are scheduled at the same time.
(If ENABLE(IDLE_GC) is on, precise GCs are disabled. Otherwise, idle GCs are disabled.)

However, we're planning to mix precise GCs and idle GCs in the near future.
At that point, a precise GC needs to be more prioritized than an idle GC.
Specifically, this CL makes a change so that a precise GC is scheduled
when an idle GC is scheduled.

BUG=474470

Review URL: https://codereview.chromium.org/1295713003

git-svn-id: svn://svn.chromium.org/blink/trunk@200706 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/platform/heap/ThreadState.cpp

@@ -650,8 +650,6 @@ bool ThreadState::shouldScheduleIdleGC()
 
 bool ThreadState::shouldSchedulePreciseGC()
 {
-    if (gcState() != NoGCScheduled)
-        return false;
 #if ENABLE(IDLE_GC)
     return false;
 #else