base: Add soft memory limit to DiscardableMemoryManager.

content/renderer/render_thread_impl.cc

Index: content/renderer/render_thread_impl.cc
diff --git a/content/renderer/render_thread_impl.cc b/content/renderer/render_thread_impl.cc
index c7ea9c71e78c6fcd3727d6326465f816285e075e..b8e2372c79cc8b6098f800bea8bfd9955b6c4c5b 100644
--- a/content/renderer/render_thread_impl.cc
+++ b/content/renderer/render_thread_impl.cc
@@ -953,6 +953,9 @@ void RenderThreadImpl::IdleHandler() {
   if (!v8::V8::IdleNotification()) {
     continue_timer = true;
   }
+  if (!base::DiscardableMemory::ReduceMemoryUsage()) {
+    continue_timer = true;
+  }
 
   // Schedule next invocation.
   // Dampen the delay using the algorithm (if delay is in seconds):
@@ -994,10 +997,17 @@ void RenderThreadImpl::IdleHandlerInForegroundTab() {
     int idle_hint = static_cast<int>(new_delay_ms / 10);
     if (cpu_usage < kIdleCPUUsageThresholdInPercents) {
       base::allocator::ReleaseFreeMemory();
-      if (v8::V8::IdleNotification(idle_hint)) {
-        // V8 finished collecting garbage.
+
+      bool finished_idle_work = true;
+      if (!v8::V8::IdleNotification(idle_hint))
+        finished_idle_work = false;
+      if (!base::DiscardableMemory::ReduceMemoryUsage())
+        finished_idle_work = false;
+
+      // V8 finished collecting garbage and discardable memory system has no
+      // more idle work left.
+      if (finished_idle_work)
         new_delay_ms = kLongIdleHandlerDelayMs;
-      }
     }
   }
   ScheduleIdleHandler(new_delay_ms);