Upstream chromium side of modal dialogs for webview.

android_webview/java/src/org/chromium/android_webview/AwContentsClient.java

Index: android_webview/java/src/org/chromium/android_webview/AwContentsClient.java
diff --git a/android_webview/java/src/org/chromium/android_webview/AwContentsClient.java b/android_webview/java/src/org/chromium/android_webview/AwContentsClient.java
index bcd0d19f9a21d2307e69a9ded1d9f14039790300..4a4233d9712570f3a0f978633f31b882df4789b3 100644
--- a/android_webview/java/src/org/chromium/android_webview/AwContentsClient.java
+++ b/android_webview/java/src/org/chromium/android_webview/AwContentsClient.java
@@ -33,7 +33,6 @@ public abstract class AwContentsClient extends ContentViewClient {
     //--------------------------------------------------------------------------------------------
 
     class WebContentsDelegateAdapter extends AwWebContentsDelegate {
-
         @Override
         public void onLoadProgressChanged(int progress) {
             AwContentsClient.this.onProgressChanged(progress);
@@ -123,6 +122,16 @@ public abstract class AwContentsClient extends ContentViewClient {
     public abstract void onReceivedHttpAuthRequest(AwHttpAuthHandler handler,
             String host, String realm);
 
+    protected abstract void handleJsAlert(String url, String message, JsResultReceiver receiver);
+
+    protected abstract void handleJsBeforeUnload(String url, String message,
+                                                 JsResultReceiver receiver);
+
+    protected abstract void handleJsConfirm(String url, String message, JsResultReceiver receiver);
+
+    protected abstract void handleJsPrompt(String url, String message, String defaultValue,
+            JsPromptResultReceiver receiver);
+
     //--------------------------------------------------------------------------------------------
     //             Stuff that we ignore since it only makes sense for Chrome browser
     //--------------------------------------------------------------------------------------------