Adds MemoryPressureListener.

base/android/java/src/org/chromium/base/MemoryPressure.java

Index: base/android/java/src/org/chromium/base/MemoryPressure.java
diff --git a/base/android/java/src/org/chromium/base/MemoryPressure.java b/base/android/java/src/org/chromium/base/MemoryPressure.java
new file mode 100644
index 0000000000000000000000000000000000000000..95c8f37505eab3139eadbea28c09dc38597c95d3
--- /dev/null
+++ b/base/android/java/src/org/chromium/base/MemoryPressure.java
@@ -0,0 +1,49 @@
+// Copyright (c) 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package org.chromium.base;
+
+import android.content.ComponentCallbacks2;
+import android.content.Context;
+import android.content.res.Configuration;
+
+import org.chromium.base.MemoryPressureLevelList;
+
+
+/**
+ * This is an internal implementation of the C++ counterpart.
+ * It registers a ComponentCallbacks2 with the system, and dispatches into
+ * native.
+ */
+class MemoryPressureHandler {
+  @CalledByNative
+  private static void registerSystemCallback(Context context) {
+      context.registerComponentCallbacks(
+          new ComponentCallbacks2() {
+                @Override
+                public void onTrimMemory(int level) {
+                    nativeOnMemoryPressure(translate(level));
+                }
+
+                @Override
+                public void onLowMemory() {
+                    nativeOnMemoryPressure(MemoryPressureLevelList.MEMORY_PRESSURE_CRITICAL);
+                }
+
+                @Override
+                public void onConfigurationChanged(Configuration configuration) {
+                }
+          });
+  }
+
+  private static int translate(int level) {
+      if (level == ComponentCallbacks2.TRIM_MEMORY_BACKGROUND ||
+          level == ComponentCallbacks2.TRIM_MEMORY_UI_HIDDEN) {

[joth, 2013/06/06 22:36:46]

I dunno. This will map UI_HIDDEN => MODERATE, but TRIM_MEMORY_RUNNING_MODERATE
=> CRITICAL.

The former is a great time to drop e.g. large bitmap allocations, but the latter
isn't (if they're still in use on screen).
How's this going to hang together?

[bulach, 2013/06/07 11:06:58]

agreed. I called out the critical level here
(ComponentCallbacks2.TRIM_MEMORY_COMPLETE), and then everything else will be
mapped to moderate.
note that onLowMemory() is also critical.

+          return MemoryPressureLevelList.MEMORY_PRESSURE_MODERATE;
+      }
+      return MemoryPressureLevelList.MEMORY_PRESSURE_CRITICAL;
+  }
+
+  private static native void nativeOnMemoryPressure(int memoryPressureType);
+}