The Browser object represents the top-level Chrome browser window. One or more
tabs (WebContents) are then owned by the Browser object via TabStripModel. A
new Browser object can be created programmatically using "new Browser" or
Browser::Create, or as a result of user action such as dragging a tab out of an
existing window. New or existing tabs can also be added to an already existing
Browser object.
The Browser object acts as the WebContentsDelegate for all attached tabs. CEF
integration requires WebContentsDelegate callbacks and notification of tab
attach/detach. To support this integration we add a cef::BrowserDelegate
(ChromeBrowserDelegate) member that is created in the Browser constructor and
receives delegation for the Browser callbacks. ChromeBrowserDelegate creates a
new ChromeBrowserHostImpl when a tab is added to a Browser for the first time,
and that ChromeBrowserHostImpl continues to exist until the tab's WebContents
is destroyed. The associated WebContents object does not change, but the
Browser object will change when the tab is dragged between windows.
CEF callback logic is shared between the chrome and alloy runtimes where
possible. This shared logic has been extracted from CefBrowserHostImpl to
create new CefBrowserHostBase and CefBrowserContentsDelegate classes. The
CefBrowserHostImpl class is now only used with the alloy runtime and will be
renamed to AlloyBrowserHostImpl in a future commit.
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