Add "previewing on hover" support for single-field autocomplete input

components/autofill/content/renderer/autofill_agent.cc

Index: components/autofill/content/renderer/autofill_agent.cc
diff --git a/components/autofill/content/renderer/autofill_agent.cc b/components/autofill/content/renderer/autofill_agent.cc
index 85f4fad689dba9c397ecd85020a124a18a65f86d..b4a6835394dc366f8f8ce7dd61b5c1441a0fe9ce 100644
--- a/components/autofill/content/renderer/autofill_agent.cc
+++ b/components/autofill/content/renderer/autofill_agent.cc
@@ -150,6 +150,8 @@ bool AutofillAgent::OnMessageReceived(const IPC::Message& message) {
                         OnSetAutofillActionPreview)
     IPC_MESSAGE_HANDLER(AutofillMsg_ClearPreviewedForm, OnClearPreviewedForm)
     IPC_MESSAGE_HANDLER(AutofillMsg_SetNodeText, OnSetNodeText)
+    IPC_MESSAGE_HANDLER(AutofillMsg_PreviewAutoCompleteNode,
+                        OnPreviewAutoCompleteNode)
     IPC_MESSAGE_HANDLER(AutofillMsg_AcceptDataListSuggestion,
                         OnAcceptDataListSuggestion)
     IPC_MESSAGE_HANDLER(AutofillMsg_AcceptPasswordAutofillSuggestion,
@@ -442,6 +444,7 @@ void AutofillAgent::OnClearPreviewedForm() {
       return;
 
     ClearPreviewedFormWithElement(element_, was_query_node_autofilled_);
+    element_.setSuggestedValue(WebString());

[Ilya Sherman, 2014/02/22 05:59:51]

Hmm, is this line actually necessary?  It seems like
ClearPreviewedFormWithElement() ought to already take care of this.

[ziran.sun, 2014/02/27 15:38:11]

Done.

   } else {
     // TODO(isherman): There seem to be rare cases where this code *is*
     // reachable: see [ http://crbug.com/96321#c6 ].  Ideally we would
@@ -456,6 +459,10 @@ void AutofillAgent::OnSetNodeText(const base::string16& value) {
   SetNodeText(value, &element_);
 }
 
+void AutofillAgent::OnPreviewAutoCompleteNode(const base::string16& value) {
+   PreviewAutoCompleteNode(value, &element_);

[Ilya Sherman, 2014/02/22 05:59:51]

nit: Why not just inline the implementation here?

[ziran.sun, 2014/02/27 15:38:11]

Done.

+}
+
 void AutofillAgent::OnAcceptDataListSuggestion(const base::string16& value) {
   AcceptDataListSuggestion(value);
 }
@@ -615,6 +622,14 @@ void AutofillAgent::SetNodeText(const base::string16& value,
   node->setEditingValue(substring);
 }
 
+void AutofillAgent::PreviewAutoCompleteNode(const base::string16& value,
+                                            blink::WebInputElement* node) {
+  base::string16 substring = value;
+  substring = substring.substr(0, node->maxLength());
+
+  node->setSuggestedValue(substring);

[Ilya Sherman, 2014/02/22 05:59:51]

You should also set 

  was_query_node_autofilled_ = element_.isAutofilled();

and set the node to have the autofilled appearance while it being previewed.

[Ilya Sherman, 2014/02/22 05:59:51]

Wow, the method you're cribbing from was needlessly verbose.  I'm fixing it in [
https://codereview.chromium.org/176213002 ].  Please update this method
similarly.

[ziran.sun, 2014/02/27 15:38:11]

Done.

+}
+
 void AutofillAgent::HideAutofillUI() {
   if (!element_.isNull())
     OnClearPreviewedForm();