Add saveImageFromDataURL() and use it in saveImageAt().

Source/web/WebViewImpl.cpp

Index: Source/web/WebViewImpl.cpp
diff --git a/Source/web/WebViewImpl.cpp b/Source/web/WebViewImpl.cpp
index fe75efa439e4122e361ec150254cbce64f7698ea..1402991d2b3ad4b3f3c5b109e3c385e99694c093 100644
--- a/Source/web/WebViewImpl.cpp
+++ b/Source/web/WebViewImpl.cpp
@@ -3296,18 +3296,14 @@ void WebViewImpl::copyImageAt(const WebPoint& point)
 
 void WebViewImpl::saveImageAt(const WebPoint& point)
 {
-    if (!m_page)
+    if (!m_client)
         return;
 
-    KURL url = hitTestResultForWindowPos(point).absoluteImageURLIncludingCanvasDataURL();
-
-    if (url.isEmpty())
+    Node* node = hitTestResultForWindowPos(point).innerNonSharedNode();
+    if (!node || !(isHTMLCanvasElement(*node) || isHTMLImageElement(*node)))
         return;
 
-    ResourceRequest request(url);
-    request.setRequestContext(WebURLRequest::RequestContextDownload);
-    m_page->deprecatedLocalMainFrame()->loader().client()->loadURLExternally(
-        request, NavigationPolicyDownloadTo, WebString());
+    m_client->saveImageFromDataURL(toElement(*node).imageSourceURL());

[Justin Novosad, 2014/09/03 16:55:29]

The name "saveImageFromDataURL" is misleading. The imageSourceURL will not be a
data URL is the node is an image element. That should be fixed in the companion
chromium-side change.

[Ken Russell (switch to Gerrit), 2014/09/04 00:23:10]

After considering the various alternatives I think this code should invoke the
old code path for images, and use this new API only for data: URLs. That has the
least possible security impact. It should still allow some of the old code to be
deleted; just not the NavigationPolicyDownloadTo enum.

 }
 
 void WebViewImpl::dragSourceEndedAt(