Migrate ChromeOS to base::MemoryPressureMonitor

chromeos/chromeos_switches.h

Index: chromeos/chromeos_switches.h
diff --git a/chromeos/chromeos_switches.h b/chromeos/chromeos_switches.h
index 1c21f0cb13bbe1f1d0b0e45357dcf6ce67707794..86b08c81fc2e585a2f393858511798461ca2f6ba 100644
--- a/chromeos/chromeos_switches.h
+++ b/chromeos/chromeos_switches.h
@@ -5,7 +5,6 @@
 #ifndef CHROMEOS_CHROMEOS_SWITCHES_H_
 #define CHROMEOS_CHROMEOS_SWITCHES_H_
 
-#include "base/chromeos/memory_pressure_observer_chromeos.h"
 #include "chromeos/chromeos_export.h"
 
 namespace chromeos {
@@ -114,8 +113,27 @@ CHROMEOS_EXPORT extern const char kDisableWebviewSigninFlow[];
 CHROMEOS_EXPORT bool WakeOnWifiEnabled();
 
 CHROMEOS_EXPORT bool MemoryPressureHandlingEnabled();
-CHROMEOS_EXPORT base::MemoryPressureObserverChromeOS::MemoryPressureThresholds
-GetMemoryPressureThresholds();
+
+// There are two memory pressure events:
+// MODERATE - which will mainly release caches.
+// CRITICAL - which will discard tabs.
+// The |MemoryPressureThresholds| enum selects the strategy of firing these
+// events: A conservative strategy will keep as much content in memory as
+// possible (causing the system to swap to zram) and an aggressive strategy
+// will release memory earlier to avoid swapping.
+enum MemoryPressureThresholds {
+  // Use the system default.
+  THRESHOLD_DEFAULT = 0,
+  // Try to keep as much content in memory as possible.
+  THRESHOLD_CONSERVATIVE = 1,
+  // Discard caches earlier, allowing to keep more tabs in memory.
+  THRESHOLD_AGGRESSIVE_CACHE_DISCARD = 2,
+  // Discard tabs earlier, allowing the system to get faster.
+  THRESHOLD_AGGRESSIVE_TAB_DISCARD = 3,
+  // Discard caches and tabs earlier to allow the system to be faster.
+  THRESHOLD_AGGRESSIVE = 4
+};
+CHROMEOS_EXPORT MemoryPressureThresholds GetMemoryPressureThresholds();
 
 }  // namespace switches
 }  // namespace chromeos