Encode visible tab on historymap

[Yuu-Han]

This helps to locate the current tab on historymap.

[Yuu-Han]

b0b1136

When a tab is activated, try to locate the page in hmPages

• If the page is found (same tab id, same url), set the node as visible and scroll to it
• Otherwise, add a virtual node to the bottom of the hm tree
  • How to save the node? Automatically add it to the array or let the user decide?
• Related to Remind user when a new tab use the same URL as an existing one. #171, ideally if a page with the same url but different tab id is found, we should remind the user.

Issues:

• The chrome.tabs.onActivated event might be fired earlier than chrome.webNavigation.onCommitted event. In this case, when a new page is opened, both the newly added node and the virtual node are displayed.
  • Fixed, not using virtual node (ffc7522), update visibility of reopened page (d2b1369)
• The visible node is not updated when the new page is opened in the same tab (as no new tab is created, there is no tab activate event).
  • Fixed (504b0fd, fb35d86)

[kaidatavis]

Is it possible that an activated tab is not a node in history map?

[Yuu-Han]

Yes. The current behaviour is adding a virtual node.

• Otherwise, add a virtual node to the bottom of the hm tree
  • How to save the node? Automatically add it to the array or let the user decide?

I haven't decided whether to directly add it to hmPages or add on user's demand.

[Yuu-Han]

Decision: add the page to hmPages on activating the tab.

[Yuu-Han]

Fixed issues in #169 (comment).