- Factor platform-specific code out of CefBrowserHostImpl (issue #1749).

- Introduce native/ and osr/ folders for native (non-platform-agnostic) and
    osr (windowless) code respectively.
  - Introduce CefBrowserPlatformDelegate for abstracting platform-specific
    implementations of browser host functionality.
  - Move dialog and menu code to separate manager and platform-specific runner
    implementations exposed via CefBrowserPlatformDelegate.
  - Standardize focus-handling behavior between windowed and windowless
    implementations. CefFocusHandler::OnSetFocus() will now also be called for
    osr focus changes.
- Support multiple simultaneous popups (issue #1289).

libcef/browser/context.h

@@ -32,6 +32,7 @@ class PrintJobManager;
 }
 
 class CefBrowserHostImpl;
+class CefBrowserInfoManager;
 class CefMainDelegate;
 class CefTraceSubscriber;
 
@@ -97,6 +98,7 @@ class CefContext {
   scoped_ptr<CefMainDelegate> main_delegate_;
   scoped_ptr<content::ContentMainRunner> main_runner_;
   scoped_ptr<CefTraceSubscriber> trace_subscriber_;
+  scoped_ptr<CefBrowserInfoManager> browser_info_manager_;
 
   // Only accessed on the UI Thread.
   scoped_ptr<printing::PrintJobManager> print_job_manager_;