mandoline: Add back/forward support and UI.

components/web_view/public/interfaces/web_view.mojom

Index: components/web_view/public/interfaces/web_view.mojom
diff --git a/components/web_view/public/interfaces/web_view.mojom b/components/web_view/public/interfaces/web_view.mojom
index 3eb490ee6d32513f4fc15254166e4772c8e47eef..f5fed45953c01f46f5da3f7f3eb78c2b628e3eed 100644
--- a/components/web_view/public/interfaces/web_view.mojom
+++ b/components/web_view/public/interfaces/web_view.mojom
@@ -14,6 +14,7 @@ interface WebViewClient {
   // Loading and progress notifications.
   LoadingStateChanged(bool is_loading);
   ProgressChanged(double progress);
+  BackForwardChanged(bool back_enabled, bool forward_enabled);

[msw, 2015/09/04 22:05:00]

nit: Backward in function and arg names to match forward.

 
   // TODO(beng): also forward text direction.
   TitleChanged(string? title);
@@ -25,6 +26,10 @@ interface WebView {
 
   // Provide a ViewTreeClient for this specific WebView.
   GetViewTreeClient(mojo.ViewTreeClient& view_tree_client);
+
+  // Moves forward and backwards.

[msw, 2015/09/04 22:05:00]

nit: match trailing 's' chars (ie. use "forwards" or "backward")

+  GoBack();

[msw, 2015/09/04 22:05:00]

nit: "GoBackward" to match "GoForward"

+  GoForward();

[msw, 2015/09/04 22:05:00]

q: Would it make sense to have a single function that takes an offset into the
navigation stack? ie. GoBackwardOrForward(int offset); That would allow jumps 2+
navigations backward/forward without iterating here. (like chrome's drop down
backward/forward menu buttons)

[Elliot Glaysher, 2015/09/04 22:54:48]

Perhaps farther down the road. For now, though I'd like to keep it this way
because it's much easier to reason about.

[msw, 2015/09/04 23:49:00]

Eh, I'd argue the opposite, but not strongly, so I'll acquiesce.

 };
 
 interface WebViewFactory {