Implement "Save image as" for canvas (blink side).

Source/web/WebViewImpl.cpp

Index: Source/web/WebViewImpl.cpp
diff --git a/Source/web/WebViewImpl.cpp b/Source/web/WebViewImpl.cpp
index a070e5041f681efab4e87a51916b0604875b92c4..6d87b6d7cad1e667a8a364390b97caff19e097f5 100644
--- a/Source/web/WebViewImpl.cpp
+++ b/Source/web/WebViewImpl.cpp
@@ -3184,6 +3184,21 @@ void WebViewImpl::copyImageAt(const WebPoint& point)
     m_page->mainFrame()->editor().copyImage(result);
 }
 
+void WebViewImpl::saveImageAt(const WebPoint& point)
+{
+    if (!m_page)
+        return;
+
+    KURL url = hitTestResultForWindowPos(point).absoluteImageURL();
+
+    if (url.isEmpty())
+        return;
+
+    ResourceRequest request(url);
+    m_page->mainFrame()->loader().client()->loadURLExternally(
+        request, NavigationPolicyDownloadTo, WebString());
+}
+
 void WebViewImpl::dragSourceEndedAt(
     const WebPoint& clientPoint,
     const WebPoint& screenPoint,