Purge browser cache for dom storage in a smarter way

content/browser/dom_storage/dom_storage_context_wrapper.h

Index: content/browser/dom_storage/dom_storage_context_wrapper.h
diff --git a/content/browser/dom_storage/dom_storage_context_wrapper.h b/content/browser/dom_storage/dom_storage_context_wrapper.h
index 17796ff8bb56bd80895e57c457fc26108d901169..06036799df6e87f66812fb4598117a735e812ee3 100644
--- a/content/browser/dom_storage/dom_storage_context_wrapper.h
+++ b/content/browser/dom_storage/dom_storage_context_wrapper.h
@@ -9,6 +9,7 @@
 #include <string>
 
 #include "base/macros.h"
+#include "base/memory/memory_pressure_listener.h"
 #include "base/memory/ref_counted.h"
 #include "content/common/content_export.h"
 #include "content/common/storage_partition_service.mojom.h"
@@ -73,6 +74,10 @@ class CONTENT_EXPORT DOMStorageContextWrapper :
                         mojom::LevelDBObserverPtr observer,
                         mojom::LevelDBWrapperRequest request);
 
+  // Called when the system is under memory pressure.
+  void OnMemoryPressure(
+      base::MemoryPressureListener::MemoryPressureLevel memory_pressure_level);
+
  private:
   friend class DOMStorageMessageFilter;  // for access to context()
   friend class SessionStorageNamespaceImpl;  // ditto
@@ -88,6 +93,8 @@ class CONTENT_EXPORT DOMStorageContextWrapper :
 
   scoped_refptr<DOMStorageContextImpl> context_;
 
+  std::unique_ptr<base::MemoryPressureListener> memory_pressure_listener_;
+
   DISALLOW_IMPLICIT_CONSTRUCTORS(DOMStorageContextWrapper);
 };