Re-land: 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 37fa09009169697a343cce73cfb9779f66e49937..daff6bc8dad3e7622981b6244ebe279ee38a3540 100644
--- a/content/renderer/render_thread_impl.cc
+++ b/content/renderer/render_thread_impl.cc
@@ -15,6 +15,7 @@
 #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"
@@ -179,6 +180,9 @@ const int kMaxRasterThreads = 64;
 // 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> >
@@ -545,10 +549,6 @@ void RenderThreadImpl::Init() {
 
   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.
   allocate_gpu_memory_buffer_thread_checker_.DetachFromThread();
@@ -1623,6 +1623,12 @@ void RenderThreadImpl::WidgetHidden() {
   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);
   }