Reduce GPU watchdog polling frequency

Reduce GPU watchdog's polling interval from 2 seconds to 5 seconds.
Also remove unnecessary CheckArmed() call from DidProcessTask(). Although
CheckArmed() checks first whether it needs to post the task, WillProcessTask
and DidProcessTask is called so quickly that armed() still returns true, so we
ended up posting the task twice most of the time.

BUG=483622

Review URL: https://codereview.chromium.org/1133703002

Cr-Commit-Position: refs/heads/master@{#329709}

content/gpu/gpu_watchdog_thread.cc

@@ -21,7 +21,6 @@
 
 namespace content {
 namespace {
-const int64 kCheckPeriodMs = 2000;
 #if defined(OS_CHROMEOS)
 const base::FilePath::CharType
     kTtyFilePath[] = FILE_PATH_LITERAL("/sys/class/tty/tty0/active");
@@ -113,7 +112,6 @@ void GpuWatchdogThread::GpuWatchdogTaskObserver::WillProcessTask(
 
 void GpuWatchdogThread::GpuWatchdogTaskObserver::DidProcessTask(
     const base::PendingTask& pending_task) {
-  watchdog_->CheckArmed();
 }
 
 GpuWatchdogThread::~GpuWatchdogThread() {
@@ -168,7 +166,7 @@ void GpuWatchdogThread::OnAcknowledge() {
       FROM_HERE,
       base::Bind(&GpuWatchdogThread::OnCheck, weak_factory_.GetWeakPtr(),
           was_suspended),
-      base::TimeDelta::FromMilliseconds(kCheckPeriodMs));
+      0.5 * timeout_);
 }
 
 void GpuWatchdogThread::OnCheck(bool after_suspend) {