[Feed] Trim stream under memory pressure

Register a MemoryPressureListener and trim the Stream memory when a
memory pressure signal is received.

BUG=860049

Change-Id: I60c7669649c1e085e0de7610fbf45b10ba327c53
Reviewed-on: https://chromium-review.googlesource.com/1178894
Commit-Queue: Theresa <twellington@chromium.org>
Reviewed-by: Becky Zhou <huayinz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#584115}

chrome/android/feed/core/java/src/org/chromium/chrome/browser/feed/FeedNewTabPageMediator.java

@@ -10,6 +10,8 @@ import com.google.android.libraries.feed.api.stream.ContentChangedListener;
 import com.google.android.libraries.feed.api.stream.ScrollListener;
 import com.google.android.libraries.feed.api.stream.Stream;
 
+import org.chromium.base.MemoryPressureListener;
+import org.chromium.base.memory.MemoryPressureCallback;
 import org.chromium.chrome.R;
 import org.chromium.chrome.browser.ntp.NewTabPageLayout;
 import org.chromium.chrome.browser.ntp.SnapScrollHelper;
@@ -30,6 +32,7 @@ class FeedNewTabPageMediator implements NewTabPageLayout.ScrollDelegate {
     private ScrollListener mStreamScrollListener;
     private ContentChangedListener mStreamContentChangedListener;
     private SectionHeader mSectionHeader;
+    private MemoryPressureCallback mMemoryPressureCallback;
 
     private boolean mStreamContentChanged;
     private int mThumbnailWidth;
@@ -55,6 +58,7 @@ class FeedNewTabPageMediator implements NewTabPageLayout.ScrollDelegate {
         stream.removeScrollListener(mStreamScrollListener);
         stream.removeOnContentChangedListener(mStreamContentChangedListener);
         mPrefChangeRegistrar.destroy();
+        MemoryPressureListener.removeCallback(mMemoryPressureCallback);
     }
 
     /**
@@ -92,6 +96,9 @@ class FeedNewTabPageMediator implements NewTabPageLayout.ScrollDelegate {
                         this::onSectionHeaderToggled);
         mCoordinator.getSectionHeaderView().setHeader(mSectionHeader);
         stream.setStreamContentVisibility(mSectionHeader.isExpanded());
+
+        mMemoryPressureCallback = pressure -> mCoordinator.getStream().trim();
+        MemoryPressureListener.addCallback(mMemoryPressureCallback);
     }
 
     /** Update whether the section header should be expanded. */

chrome/android/javatests/src/org/chromium/chrome/browser/ntp/NewTabPageTest.java

@@ -11,6 +11,7 @@ import static android.support.test.espresso.matcher.ViewMatchers.withId;
 import android.app.Activity;
 import android.app.Instrumentation;
 import android.app.Instrumentation.ActivityMonitor;
+import android.content.ComponentCallbacks2;
 import android.graphics.Canvas;
 import android.support.test.InstrumentationRegistry;
 import android.support.test.filters.LargeTest;
@@ -28,7 +29,9 @@ import org.junit.Rule;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 
+import org.chromium.base.MemoryPressureListener;
 import org.chromium.base.ThreadUtils;
+import org.chromium.base.memory.MemoryPressureCallback;
 import org.chromium.base.test.params.ParameterAnnotations;
 import org.chromium.base.test.params.ParameterProvider;
 import org.chromium.base.test.params.ParameterSet;
@@ -737,6 +740,27 @@ public class NewTabPageTest {
         mRenderTestRule.render(view, "expandable_header_collapsed");
     }
 
+    @Test
+    @SmallTest
+    @Feature({"NewTabPage", "FeedNewTabPage"})
+    @ParameterAnnotations.UseMethodParameter(InterestFeedParams.class)
+    public void testMemoryPressure(boolean interestFeedEnabled) throws Exception {
+        // TODO(twellington): This test currently just checks that sending a memory pressure
+        // signal doesn't crash. Enhance the test to also check whether certain behaviors are
+        // performed.
+        CallbackHelper callback = new CallbackHelper();
+        MemoryPressureCallback pressureCallback = pressure -> callback.notifyCalled();
+        ThreadUtils.runOnUiThreadBlocking(() -> {
+            MemoryPressureListener.addCallback(pressureCallback);
+            mActivityTestRule.getActivity().getApplication().onTrimMemory(
+                    ComponentCallbacks2.TRIM_MEMORY_MODERATE);
+        });
+
+        callback.waitForCallback(0);
+        ThreadUtils.runOnUiThreadBlocking(
+                () -> MemoryPressureListener.removeCallback(pressureCallback));
+    }
+
     private void assertThumbnailInvalidAndRecapture() {
         Assert.assertTrue(mNtp.shouldCaptureThumbnail());
         captureThumbnail();