Use UndoDebuggerSuspensions for JDWP ResumeVM rather than weakening ResumeAll's checking.

Change-Id: I3ba71fb9e84664f130dd29ba8c13a8e1b6c18e46
diff --git a/src/debugger.cc b/src/debugger.cc
index 1dbcccc..604560e 100644
--- a/src/debugger.cc
+++ b/src/debugger.cc
@@ -1525,7 +1525,7 @@
 }
 
 void Dbg::ResumeVM() {
-  Runtime::Current()->GetThreadList()->ResumeAll(true);
+  Runtime::Current()->GetThreadList()->UndoDebuggerSuspensions();
 }
 
 void Dbg::SuspendThread(JDWP::ObjectId threadId) {