Make GC test catch strong ref from client objects

In the public sdk API, apps should be able to hold a strong WebView
reference from WebChromeClient or WebViewClient, without having to worry
about preventing WebView from gc-ed.

Simulate that behavior in testCreateAndGcManyTimes by having the
AwContentsClient hold a strong reference to AwContents.

And remove the strong ref from AwWebContentsObserver to
make the test pass.

BUG=469803

Review URL: https://codereview.chromium.org/1036893002

Cr-Commit-Position: refs/heads/master@{#322380}

android_webview/java/src/org/chromium/android_webview/AwWebContentsObserver.java

@@ -23,14 +23,14 @@ public class AwWebContentsObserver extends WebContentsObserver {
     // reference to an AwWebContentsObserver instance. This is not intentional,
     // and should be found and cleaned up.
     private final WeakReference<AwContents> mAwContents;
-    private final AwContentsClient mAwContentsClient;
+    private final WeakReference<AwContentsClient> mAwContentsClient;
     private boolean mStartedNonApiProvisionalLoadInMainFrame = false;
 
     public AwWebContentsObserver(
             WebContents webContents, AwContents awContents, AwContentsClient awContentsClient) {
         super(webContents);
-        mAwContents = new WeakReference<AwContents>(awContents);
-        mAwContentsClient = awContentsClient;
+        mAwContents = new WeakReference<>(awContents);
+        mAwContentsClient = new WeakReference<>(awContentsClient);
     }
 
     boolean hasStartedNonApiProvisionalLoadInMainFrame() {
@@ -39,24 +39,28 @@ public class AwWebContentsObserver extends WebContentsObserver {
 
     @Override
     public void didFinishLoad(long frameId, String validatedUrl, boolean isMainFrame) {
+        AwContentsClient client = mAwContentsClient.get();
+        if (client == null) return;
         String unreachableWebDataUrl = AwContentsStatics.getUnreachableWebDataUrl();
         boolean isErrorUrl =
                 unreachableWebDataUrl != null && unreachableWebDataUrl.equals(validatedUrl);
         if (isMainFrame && !isErrorUrl) {
-            mAwContentsClient.onPageFinished(validatedUrl);
+            client.onPageFinished(validatedUrl);
         }
     }
 
     @Override
     public void didFailLoad(boolean isProvisionalLoad,
             boolean isMainFrame, int errorCode, String description, String failingUrl) {
+        AwContentsClient client = mAwContentsClient.get();
+        if (client == null) return;
         String unreachableWebDataUrl = AwContentsStatics.getUnreachableWebDataUrl();
         boolean isErrorUrl =
                 unreachableWebDataUrl != null && unreachableWebDataUrl.equals(failingUrl);
         if (isMainFrame && !isErrorUrl && errorCode == NetError.ERR_ABORTED) {
             // Need to call onPageFinished for backwards compatibility with the classic webview.
             // See also AwContents.IoThreadClientImpl.onReceivedError.
-            mAwContentsClient.onPageFinished(failingUrl);
+            client.onPageFinished(failingUrl);
         }
     }
 
@@ -74,23 +78,30 @@ public class AwWebContentsObserver extends WebContentsObserver {
                         awContents.insertVisualStateCallback(0, new VisualStateCallback() {
                             @Override
                             public void onComplete(long requestId) {
-                                mAwContentsClient.onPageCommitVisible(url);
+                                AwContentsClient client = mAwContentsClient.get();
+                                if (client == null) return;
+                                client.onPageCommitVisible(url);
                             }
                         });
                     }
                 }
             });
         }
+
         // This is here to emulate the Classic WebView firing onPageFinished for main frame
         // navigations where only the hash fragment changes.
         if (isFragmentNavigation) {
-            mAwContentsClient.onPageFinished(url);
+            AwContentsClient client = mAwContentsClient.get();
+            if (client == null) return;
+            client.onPageFinished(url);
         }
     }
 
     @Override
     public void didNavigateAnyFrame(String url, String baseUrl, boolean isReload) {
-        mAwContentsClient.doUpdateVisitedHistory(url, isReload);
+        final AwContentsClient client = mAwContentsClient.get();
+        if (client == null) return;
+        client.doUpdateVisitedHistory(url, isReload);
     }
 
     @Override

android_webview/javatests/src/org/chromium/android_webview/test/AwContentsTest.java

@@ -139,6 +139,14 @@ public class AwContentsTest extends AwTestBase {
                 new KeyEvent(KeyEvent.ACTION_DOWN, KeyEvent.KEYCODE_MENU));
     }
 
+    @SuppressFBWarnings("URF_UNREAD_FIELD")
+    private static class StrongRefTestAwContentsClient extends TestAwContentsClient {
+        private AwContents mAwContentsStrongRef;
+        public void setAwContentsStrongRef(AwContents awContents) {
+            mAwContentsStrongRef = awContents;
+        }
+    }
+
     @DisableHardwareAccelerationForTest
     @LargeTest
     @Feature({"AndroidWebView"})
@@ -159,7 +167,13 @@ public class AwContentsTest extends AwTestBase {
         });
         for (int i = 0; i < repetitions; ++i) {
             for (int j = 0; j < concurrentInstances; ++j) {
-                AwTestContainerView view = createAwTestContainerViewOnMainSync(mContentsClient);
+                final StrongRefTestAwContentsClient client = new StrongRefTestAwContentsClient();
+                AwTestContainerView view = createAwTestContainerViewOnMainSync(client);
+                // Embedding app can hold onto a strong ref to the WebView from either WebViewClient
+                // or WebChromeClient. That should not prevent WebView from gc-ed. We simulate that
+                // behavior by making the equivalent change here, have AwContentsClient hold a
+                // strong ref to the AwContents object.
+                client.setAwContentsStrongRef(view.getAwContents());
                 loadUrlAsync(view.getAwContents(), "about:blank");
             }
             assertTrue(AwContents.getNativeInstanceCount() >= concurrentInstances);