Hook up PA_LOG() logs to chrome://proximity-auth WebUI.

components/proximity_auth/webui/proximity_auth_webui_handler.h

Index: components/proximity_auth/webui/proximity_auth_webui_handler.h
diff --git a/components/proximity_auth/webui/proximity_auth_webui_handler.h b/components/proximity_auth/webui/proximity_auth_webui_handler.h
index 8cc050895e9116cbffdfe01e1c4fabb3f5dde5ea..accd7ac8ef86581a3c3f2c05892f6f152c143736 100644
--- a/components/proximity_auth/webui/proximity_auth_webui_handler.h
+++ b/components/proximity_auth/webui/proximity_auth_webui_handler.h
@@ -5,22 +5,36 @@
 #ifndef COMPONENTS_PROXIMITY_AUTH_WEBUI_PROXIMITY_AUTH_WEBUI_HANDLER_H_
 #define COMPONENTS_PROXIMITY_AUTH_WEBUI_PROXIMITY_AUTH_WEBUI_HANDLER_H_
 
+#include "components/proximity_auth/logging/log_buffer.h"
 #include "content/public/browser/web_ui_message_handler.h"
 
+namespace base {
+class ListValue;
+}
+
 namespace proximity_auth {
 
 class ProximityAuthService;
 
 // Handles messages from the chrome://proximity-auth page.
-class ProximityAuthWebUIHandler : public content::WebUIMessageHandler {
+class ProximityAuthWebUIHandler : public content::WebUIMessageHandler,
+                                  public LogBuffer::Observer {
  public:
   ProximityAuthWebUIHandler();
   ~ProximityAuthWebUIHandler() override;
 
-  // content::WebUIMessageHandler implementation.
+  // content::WebUIMessageHandler:
   void RegisterMessages() override;
 
  private:
+  // LogBuffer::Observer:
+  void OnLogMessageAdded(const LogBuffer::LogMessage& log_message) override;
+  void OnLogBufferCleared() override;
+
+  // Message handler callbacks.
+  void GetLogMessages(const base::ListValue* args);
+  void ClearLogBuffer(const base::ListValue* args);
+
   DISALLOW_COPY_AND_ASSIGN(ProximityAuthWebUIHandler);
 };