Use ActivityManagerService global lock in dumpHeap

Bug: 187013484
Test: adb shell am dumpheap
Change-Id: I1d3d8016f228c1ee9aa82edee7550ba3e50843ae

services/core/java/com/android/server/am/ActivityManagerService.java

@@ -14831,7 +14831,7 @@ public class ActivityManagerService extends IActivityManager.Stub
                 throw new IllegalArgumentException("null fd");
             }
 
-            synchronized (mProcLock) {
+            synchronized (this) {
                 ProcessRecord proc = findProcessLOSP(process, userId, "dumpHeap");
                 IApplicationThread thread;
                 if (proc == null || (thread = proc.getThread()) == null) {