Revert of Move throttling of background timers into the renderer scheduler

third_party/WebKit/Source/core/frame/DOMTimer.cpp

Index: third_party/WebKit/Source/core/frame/DOMTimer.cpp
diff --git a/third_party/WebKit/Source/core/frame/DOMTimer.cpp b/third_party/WebKit/Source/core/frame/DOMTimer.cpp
index cdfb3d8f5ffc0a0c6a0f37921b685b11b0609312..b820cc6e840b87600fda2ae527247dedad0dc708 100644
--- a/third_party/WebKit/Source/core/frame/DOMTimer.cpp
+++ b/third_party/WebKit/Source/core/frame/DOMTimer.cpp
@@ -52,6 +52,19 @@
         && nestingLevel == 1; // Gestures should not be forwarded to nested timers.
 }
 
+double DOMTimer::hiddenPageAlignmentInterval()
+{
+    // Timers on hidden pages are aligned so that they fire once per
+    // second at most.
+    return 1.0;
+}
+
+double DOMTimer::visiblePageAlignmentInterval()
+{
+    // Alignment does not apply to timers on visible pages.
+    return 0;
+}
+
 int DOMTimer::install(ExecutionContext* context, PassOwnPtrWillBeRawPtr<ScheduledAction> action, int timeout, bool singleShot)
 {
     int timeoutID = context->timers()->installNewTimeout(context, action, timeout, singleShot);
@@ -151,6 +164,42 @@
     m_action.clear();
 }
 
+double DOMTimer::alignedFireTime(double fireTime) const
+{
+    double alignmentInterval = executionContext()->timerAlignmentInterval();
+    if (alignmentInterval) {
+        double currentTime = monotonicallyIncreasingTime();
+        if (fireTime <= currentTime)
+            return fireTime;
+
+        // When a repeating timer is scheduled for exactly the
+        // background page alignment interval, because it's impossible
+        // for the timer to be rescheduled instantaneously, it misses
+        // every other fire time. Avoid this by looking at the next
+        // fire time rounded both down and up.
+
+        double alignedTimeRoundedDown = floor(fireTime / alignmentInterval) * alignmentInterval;
+        double alignedTimeRoundedUp = ceil(fireTime / alignmentInterval) * alignmentInterval;
+
+        // If the version rounded down is in the past, discard it
+        // immediately.
+
+        if (alignedTimeRoundedDown <= currentTime)
+            return alignedTimeRoundedUp;
+
+        // Only use the rounded-down time if it's within a certain
+        // tolerance of the fire time. This avoids speeding up timers
+        // on background pages in the common case.
+
+        if (fireTime - alignedTimeRoundedDown < minimumInterval)
+            return alignedTimeRoundedDown;
+
+        return alignedTimeRoundedUp;
+    }
+
+    return fireTime;
+}
+
 WebTaskRunner* DOMTimer::timerTaskRunner()
 {
     return executionContext()->timers()->timerTaskRunner();