Free memory when the last WebView instance is destroyed.

android_webview/java/src/org/chromium/android_webview/AwContents.java

 // Copyright 2012 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.android_webview;
 
+import android.content.ComponentCallbacks2;
 import android.content.pm.PackageManager;
 import android.content.res.Configuration;
 import android.graphics.Bitmap;
 import android.graphics.Canvas;
 import android.graphics.Color;
 import android.graphics.Picture;
 import android.graphics.Rect;
 import android.graphics.drawable.Drawable;
 import android.net.http.SslCertificate;
 import android.os.AsyncTask;
@@ skipping 14 matching lines @@
 import android.view.inputmethod.EditorInfo;
 import android.view.inputmethod.InputConnection;
 import android.webkit.GeolocationPermissions;
 import android.webkit.ValueCallback;
 import android.widget.OverScroller;
 
 import com.google.common.annotations.VisibleForTesting;
 
 import org.chromium.base.CalledByNative;
 import org.chromium.base.JNINamespace;
+import org.chromium.base.MemoryPressureListener;
 import org.chromium.base.ThreadUtils;
 import org.chromium.content.browser.ContentSettings;
 import org.chromium.content.browser.ContentVideoView;
 import org.chromium.content.browser.ContentViewClient;
 import org.chromium.content.browser.ContentViewCore;
 import org.chromium.content.browser.ContentViewStatics;
 import org.chromium.content.browser.LoadUrlParams;
 import org.chromium.content.browser.NavigationHistory;
 import org.chromium.content.browser.PageTransitionTypes;
 import org.chromium.content.common.CleanupReference;
@@ skipping 136 matching lines @@
     private static final class DestroyRunnable implements Runnable {
         private int mNativeAwContents;
         private DestroyRunnable(int nativeAwContents) {
             mNativeAwContents = nativeAwContents;
         }
         @Override
         public void run() {
             // This is a no-op if not currently attached.
             nativeOnDetachedFromWindow(mNativeAwContents);
             nativeDestroy(mNativeAwContents);
+
+            // Send a memory pressure signal for freeing up some memory if this
+            // is the last WebView instance.
+            if (getNativeInstanceCount() == 0) {
+                    MemoryPressureListener.simulateMemoryPressureSignal(
+                            ComponentCallbacks2.TRIM_MEMORY_COMPLETE);

[joth, 2013/09/03 18:37:58]

It's always a bit hairy adding new code to the CleanupReference as it's very
easy to introduce memory leak.
This change looks safe. But just to check could we do this in the native d'tor
by calling  base::MemoryPressureListener::NotifyMemoryPressure() instead?

[Primiano Tucci (use gerrit), 2013/09/05 11:47:25]

Done.

+            }
         }
     }
 
     // Reference to the active mNativeAwContents pointer while it is active use
     // (ie before it is destroyed).
     private CleanupReference mCleanupReference;
 
     // A list of references to native pointers where the Java counterpart has been
     // destroyed, but are held here because they are waiting for onDetachFromWindow
     // to release GL resources. This is cleared inside onDetachFromWindow.
@@ skipping 1711 matching lines @@
 
     private native int nativeGetAwDrawGLViewContext(int nativeAwContents);
     private native int nativeCapturePicture(int nativeAwContents, int width, int height);
     private native void nativeEnableOnNewPicture(int nativeAwContents, boolean enabled);
 
     private native void nativeInvokeGeolocationCallback(
             int nativeAwContents, boolean value, String requestingFrame);
 
     private native void nativeSetJsOnlineProperty(int nativeAwContents, boolean networkUp);
 }