Revert of base: Introduce an explicit call for reducing emulated discardable memory usage.

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 ff598a07ed9cfcfc6c38b2bbf9978cb950ae2f8a..e652d229f3a8dafb4e6b58e018370886ba4de931 100644
--- a/content/renderer/render_thread_impl.cc
+++ b/content/renderer/render_thread_impl.cc
@@ -15,7 +15,6 @@
 #include "base/lazy_instance.h"
 #include "base/logging.h"
 #include "base/memory/discardable_memory.h"
-#include "base/memory/discardable_memory_emulated.h"
 #include "base/memory/shared_memory.h"
 #include "base/metrics/field_trial.h"
 #include "base/metrics/histogram.h"
@@ -179,9 +178,6 @@
 // allocation that exceeds this limit.
 const size_t kImageCacheSingleAllocationByteLimit = 64 * 1024 * 1024;
 
-const size_t kEmulatedDiscardableMemoryBytesToKeepWhenWidgetsHidden =
-    4 * 1024 * 1024;
-
 // Keep the global RenderThreadImpl in a TLS slot so it is impossible to access
 // incorrectly from the wrong thread.
 base::LazyInstance<base::ThreadLocalPointer<RenderThreadImpl> >
@@ -537,6 +533,10 @@
   }
 
   base::DiscardableMemory::SetPreferredType(type);
+
+  // Allow discardable memory implementations to register memory pressure
+  // listeners.
+  base::DiscardableMemory::RegisterMemoryPressureListeners();
 
   // AllocateGpuMemoryBuffer must be used exclusively on one thread but
   // it doesn't have to be the same thread RenderThreadImpl is created on.
@@ -1609,12 +1609,6 @@
   hidden_widget_count_++;
 
   if (widget_count_ && hidden_widget_count_ == widget_count_) {
-    // TODO(reveman): Remove this when we have a better mechanism to prevent
-    // total discardable memory used by all renderers from growing too large.
-    base::internal::DiscardableMemoryEmulated::
-        ReduceMemoryUsageUntilWithinLimit(
-            kEmulatedDiscardableMemoryBytesToKeepWhenWidgetsHidden);
-
     if (GetContentClient()->renderer()->RunIdleHandlerWhenWidgetsHidden())
       ScheduleIdleHandler(kInitialIdleHandlerDelayMs);
   }