[PM] Fix order of destruction in EnforceObserversRemoved test

R=siggi

Bug: 1150794
Change-Id: I19e926b5e791aef70bd27e8195059fd9bf3e926d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2593172
Commit-Queue: Joe Mason <joenotcharles@chromium.org>
Commit-Queue: Sigurður Ásgeirsson <siggi@chromium.org>
Auto-Submit: Joe Mason <joenotcharles@chromium.org>
Reviewed-by: Sigurður Ásgeirsson <siggi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#837193}

components/performance_manager/v8_memory/v8_detailed_memory_unittest.cc

@@ -1522,17 +1522,19 @@ TEST_F(V8DetailedMemoryDecoratorDeathTest, MultipleStartMeasurement) {
 }
 
 TEST_F(V8DetailedMemoryDecoratorDeathTest, EnforceObserversRemoved) {
+  // Declare the observers before the requests to ensure they're deleted
+  // afterwards.
   EXPECT_DCHECK_DEATH({
-    V8DetailedMemoryRequest memory_request(kMinTimeBetweenRequests);
     MockV8DetailedMemoryObserver observer;
+    V8DetailedMemoryRequest memory_request(kMinTimeBetweenRequests);
     memory_request.AddObserver(&observer);
     // Request should explode if it still has observers registered when it goes
     // out of scope.
   });
 
   EXPECT_DCHECK_DEATH({
-    V8DetailedMemoryRequestAnySeq memory_request(kMinTimeBetweenRequests);
     MockV8DetailedMemoryObserverAnySeq observer;
+    V8DetailedMemoryRequestAnySeq memory_request(kMinTimeBetweenRequests);
     memory_request.AddObserver(&observer);
     // Request should explode if it still has observers registered when it goes
     // out of scope.