memory coordinator: Add metrics for Android's onTrimMemory()

content/public/android/java/src/org/chromium/content/browser/MemoryMonitorAndroid.java

Index: content/public/android/java/src/org/chromium/content/browser/MemoryMonitorAndroid.java
diff --git a/content/public/android/java/src/org/chromium/content/browser/MemoryMonitorAndroid.java b/content/public/android/java/src/org/chromium/content/browser/MemoryMonitorAndroid.java
index 0fa1e03b42803ca14cda4b2365b932d51a39de0c..501b69c257970490fd8bb9b3689d7df8ef9d2364 100644
--- a/content/public/android/java/src/org/chromium/content/browser/MemoryMonitorAndroid.java
+++ b/content/public/android/java/src/org/chromium/content/browser/MemoryMonitorAndroid.java
@@ -5,7 +5,9 @@
 package org.chromium.content.browser;
 
 import android.app.ActivityManager;
+import android.content.ComponentCallbacks2;
 import android.content.Context;
+import android.content.res.Configuration;
 
 import org.chromium.base.annotations.CalledByNative;
 import org.chromium.base.annotations.JNINamespace;
@@ -17,6 +19,10 @@ import org.chromium.base.annotations.JNINamespace;
 class MemoryMonitorAndroid {
     private static final ActivityManager.MemoryInfo sMemoryInfo =
             new ActivityManager.MemoryInfo();
+    private static ComponentCallbacks2 sCallbacks = null;
+
+    private MemoryMonitorAndroid() {
+    }
 
     /**
      * Get the current MemoryInfo from ActivityManager and invoke the native
@@ -36,7 +42,34 @@ class MemoryMonitorAndroid {
                 sMemoryInfo.threshold, sMemoryInfo.totalMem, outPtr);
     }
 
+    /**
+     * Register ComponentCallbacks2 to receive memory pressure signals.
+     *
+     * @param context The context of the application.
+     */
+    @CalledByNative
+    private static void registerComponentCallbacks(Context context) {
+        sCallbacks = new ComponentCallbacks2() {
+                @Override
+                public void onTrimMemory(int level) {
+                    if (level != ComponentCallbacks2.TRIM_MEMORY_UI_HIDDEN) {
+                        nativeOnTrimMemory(level);
+                    }
+                }
+                @Override
+                public void onLowMemory() {
+                    // Don't support old onLowMemory().
+                }
+                @Override
+                public void onConfigurationChanged(Configuration config) {
+                }
+            };
+        context.registerComponentCallbacks(sCallbacks);
+    }
+
     private static native void nativeGetMemoryInfoCallback(
             long availMem, boolean lowMemory,
             long threshold, long totalMem, long outPtr);
+
+    private static native void nativeOnTrimMemory(int level);
 }