Free memory when the last WebView instance is destroyed.

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

Index: android_webview/java/src/org/chromium/android_webview/AwContents.java
diff --git a/android_webview/java/src/org/chromium/android_webview/AwContents.java b/android_webview/java/src/org/chromium/android_webview/AwContents.java
index 18ba0cca75fc4727e16cdad3210af97f00d3ef2c..25c17012fa32e0fb044b3ae58133cfb951bbf8a6 100644
--- a/android_webview/java/src/org/chromium/android_webview/AwContents.java
+++ b/android_webview/java/src/org/chromium/android_webview/AwContents.java
@@ -4,6 +4,7 @@
 
 package org.chromium.android_webview;
 
+import android.content.ComponentCallbacks2;
 import android.content.pm.PackageManager;
 import android.content.res.Configuration;
 import android.graphics.Bitmap;
@@ -38,6 +39,7 @@ 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;
@@ -194,6 +196,13 @@ public class AwContents {
             // 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.

+            }
         }
     }