Add DownloadControllerAndroid public interface for android.

android_webview/native/aw_web_contents_delegate.cc

Index: android_webview/native/aw_web_contents_delegate.cc
diff --git a/android_webview/native/aw_web_contents_delegate.cc b/android_webview/native/aw_web_contents_delegate.cc
index 2a04d2dd7f29f0a6521218eb4dc9085e7658e012..33e8edd88ed36b199d6a813613b3ce14291050de 100644
--- a/android_webview/native/aw_web_contents_delegate.cc
+++ b/android_webview/native/aw_web_contents_delegate.cc
@@ -8,7 +8,9 @@
 #include "android_webview/browser/find_helper.h"
 #include "android_webview/native/aw_contents.h"
 #include "android_webview/native/aw_javascript_dialog_creator.h"
+#include "content/public/browser/android/download_controller_android.h"
 #include "content/public/browser/web_contents.h"
+#include "net/http/http_request_headers.h"
 
 using content::WebContents;
 
@@ -47,4 +49,19 @@ void AwWebContentsDelegate::FindReply(WebContents* web_contents,
                                                 final_update);
 }
 
+bool AwWebContentsDelegate::CanDownload(content::RenderViewHost* source,
+                                        int request_id,
+                                        const std::string& request_method) {
+  if (request_method == net::HttpRequestHeaders::kGetMethod) {
+    content::DownloadControllerAndroid::Get()->CreateGETDownload(
+        source, request_id);
+  }
+  return false;
+}
+
+void AwWebContentsDelegate::OnStartDownload(WebContents* source,
+                                            content::DownloadItem* download) {
+  NOTREACHED();  // We always return false in CanDownload.
+}
+
 }  // namespace android_webview