Debugger: Simplify removal of outdated L&E items

This removes the need of bookkeeping on the engine side. It's
basically a kind of mark-and-sweep: On update begin mark items
that are expected to change as outdated, while data arrives, undo
that marking, and update end remove all remaining marked items.

Change-Id: I739b84869033d511d5c9a80605c079e87ef4f6a7
Reviewed-by: David Schulz <david.schulz@theqtcompany.com>

src/plugins/debugger/lldb/lldbengine.cpp

@@ -447,8 +447,8 @@ void LldbEngine::handleResponse(const QByteArray &response)
     foreach (const GdbMi &item, all.children()) {
         const QByteArray name = item.name();
         if (name == "all") {
-            watchHandler()->notifyUpdateFinished();
             updateLocalsView(item);
+            watchHandler()->notifyUpdateFinished();
         } else if (name == "dumpers") {
             watchHandler()->addDumpers(item);
             setupInferiorStage2();
@@ -864,7 +864,7 @@ void LldbEngine::doUpdateLocals(const UpdateParameters &params)
         return;
     }
 
-    watchHandler()->notifyUpdateStarted();
+    watchHandler()->notifyUpdateStarted(params.partialVariables());
 
     DebuggerCommand cmd("updateData");
     cmd.arg("nativeMixed", isNativeMixedActive());