chrome: Add callback for already running app relaunch (fixes #3609)

Adds a new CefBrowserProcessHandler::OnAlreadyRunningAppRelaunch
callback for when an already running app is relaunched with the
same CefSettings.root_cache_path.

Client apps should check the CefInitialize() return value for early
exit of the relaunch source process.

tests/cefclient/browser/main_context.h

@@ -10,6 +10,7 @@
 
 #include "include/base/cef_macros.h"
 #include "include/base/cef_ref_counted.h"
+#include "include/cef_command_line.h"
 #include "include/internal/cef_types_wrappers.h"
 #include "tests/cefclient/browser/osr_renderer_settings.h"
 
@@ -24,6 +25,9 @@ class MainContext {
   // Returns the singleton instance of this object.
   static MainContext* Get();
 
+  // Returns the global command-line.
+  virtual CefRefPtr<CefCommandLine> GetCommandLine() = 0;
+
   // Returns the full path to the console log file.
   virtual std::string GetConsoleLogPath() = 0;
 
@@ -33,8 +37,8 @@ class MainContext {
   // Returns the app working directory including trailing path separator.
   virtual std::string GetAppWorkingDirectory() = 0;
 
-  // Returns the main application URL.
-  virtual std::string GetMainURL() = 0;
+  // Returns the main application URL based on |command_line| and global state.
+  virtual std::string GetMainURL(CefRefPtr<CefCommandLine> command_line) = 0;
 
   // Returns the background color.
   virtual cef_color_t GetBackgroundColor() = 0;