Fix HandlerLeak lint warning

android_webview/glue/java/src/com/android/webview/chromium/WebViewContentsClientAdapter.java

 // Copyright 2014 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 com.android.webview.chromium;
 
 import android.annotation.TargetApi;
 import android.content.Context;
 import android.graphics.Bitmap;
 import android.graphics.BitmapFactory;
@@ skipping 92 matching lines @@
     private WebViewDelegate mWebViewDelegate;
 
     private DownloadListener mDownloadListener;
 
     private Handler mUiThreadHandler;
 
     private static final int NEW_WEBVIEW_CREATED = 100;
 
     private WeakHashMap<AwPermissionRequest, WeakReference<PermissionRequestAdapter>>
             mOngoingPermissionRequests;
+
+    private static class UiThreadHandler extends Handler {
+        private final WeakReference<WebView> mWeakWebView;

[boliu, 2016/08/24 00:36:04]

I... don't think this is safe. It's actually conceivable app isn't holding onto
the webview that created the pop up anymore, then gc could actually release it.
so the whole premise of that warning just doesn't hold

I hate these warnings, either it should be applied universally and break build,
or they should just not be turned on at all

+
+        public UiThreadHandler(WebView webView) {
+            mWeakWebView = new WeakReference<WebView>(webView);
+        }
+
+        @Override
+        public void handleMessage(Message msg) {
+            switch (msg.what) {
+                case NEW_WEBVIEW_CREATED:
+                    if (mWeakWebView.get() == null) {

[boliu, 2016/08/24 00:36:04]

this is not c++ WeakPtr, gc can run at any time, and you need to hold a strong
ref here to make sure it doesn't go away in this method

+                        return;

[Torne, 2016/08/24 15:31:36]

Just returning here would mean that even though the app *did* create a new
WebView and pass it to us from onCreateWindow, the popup will never do anything
and effectively be dead (if the app has managed to drop all strong references to
the parent WebView at that point). This doesn't seem like a desirable outcome.

I think we could only do this safely if we also invented a way to finish opening
the popup successfully with a null parent - I have no idea if that's really
possible..

[boliu, 2016/08/24 16:08:59]

It is. Have the native AwContents of the pop up be owned by the message
probably. That probably gets into a lot of weird corner cases that I'd rather
not think about too much. imo current thing is fine

I will support merging all of our handlers so there is only one. There is
another one for handling webview callbacks in AwContentsClientCallbackHelper

+                    }
+                    WebView.WebViewTransport t = (WebView.WebViewTransport) msg.obj;
+                    WebView newWebView = t.getWebView();
+                    if (newWebView == mWeakWebView.get()) {
+                        throw new IllegalArgumentException(
+                                "Parent WebView cannot host it's own popup window. Please "
+                                + "use WebSettings.setSupportMultipleWindows(false)");
+                    }
+
+                    if (newWebView != null && newWebView.copyBackForwardList().getSize() != 0) {
+                        throw new IllegalArgumentException(
+                                "New WebView for popup window must not have been previously "
+                                + "navigated.");
+                    }
+
+                    WebViewChromium.completeWindowCreation(mWeakWebView.get(), newWebView);
+                    break;
+                default:
+                    throw new IllegalStateException();
+            }
+        }
+    }
+
     /**
      * Adapter constructor.
      *
      * @param webView the {@link WebView} instance that this adapter is serving.
      */
     WebViewContentsClientAdapter(WebView webView, Context context,
             WebViewDelegate webViewDelegate) {
         if (webView == null || webViewDelegate == null) {
             throw new IllegalArgumentException("webView or delegate can't be null.");
         }
 
         if (context == null) {
             throw new IllegalArgumentException("context can't be null.");
         }
 
         mContext = context;
         mWebView = webView;
         mWebViewDelegate = webViewDelegate;
         setWebViewClient(null);
 
-        mUiThreadHandler = new Handler() {
-            @Override
-            public void handleMessage(Message msg) {
-                switch (msg.what) {
-                    case NEW_WEBVIEW_CREATED:
-                        WebView.WebViewTransport t = (WebView.WebViewTransport) msg.obj;
-                        WebView newWebView = t.getWebView();
-                        if (newWebView == mWebView) {
-                            throw new IllegalArgumentException(
-                                    "Parent WebView cannot host it's own popup window. Please "
-                                    + "use WebSettings.setSupportMultipleWindows(false)");
-                        }
-
-                        if (newWebView != null && newWebView.copyBackForwardList().getSize() != 0) {
-                            throw new IllegalArgumentException(
-                                    "New WebView for popup window must not have been previously "
-                                    + "navigated.");
-                        }
-
-                        WebViewChromium.completeWindowCreation(mWebView, newWebView);
-                        break;
-                    default:
-                        throw new IllegalStateException();
-                }
-            }
-        };
+        mUiThreadHandler = new UiThreadHandler(mWebView);
     }
 
     void setWebViewClient(WebViewClient client) {
         if (client != null) {
             mWebViewClient = client;
         } else {
             mWebViewClient = sNullWebViewClient;
         }
     }
 
@@ skipping 1113 matching lines @@
                 mAwPermissionRequest.deny();
             }
         }
 
         @Override
         public void deny() {
             mAwPermissionRequest.deny();
         }
     }
 }