Adds MemoryPressureListener.

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

Index: base/android/java/src/org/chromium/base/MemoryPressureHandler.java
diff --git a/base/android/java/src/org/chromium/base/MemoryPressureHandler.java b/base/android/java/src/org/chromium/base/MemoryPressureHandler.java
new file mode 100644
index 0000000000000000000000000000000000000000..744d1f187229b24166d4900a945cc5d790e77283
--- /dev/null
+++ b/base/android/java/src/org/chromium/base/MemoryPressureHandler.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.MemoryPressureList;
+
+
+/**
+ * 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(MemoryPressureList.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, 2013/06/05 19:49:48]

oh, hmmm, yeah we may find it very useful to have this global background-ness
connected through too for GL resource release. I totally forgot this info was
included here.

We haven't a firm idea on the policy details there yet though, so maybe we come
back and iterate more on. (Worse case we just register our own
ComponentCallbacks2 instance for that I guess)

[bulach, 2013/06/06 09:28:30]

should this perhaps expose the native call? that is, other modules could plug
their listeners in their java code however they want? (of course, I mean, expose
a static java wrapper function here, not the native directly..)

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

Just to avoid having two different ComponentCallbacks2 classes instantiated? not
sure it's worth it - we can always add a public API in future when needed.

The question here was more if we should add more of the levels to
MemoryPressureList

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