Add tests for calling {Suspend,Resume}Renderer() on foreground renderer

This is a follow-up CL of crrev.com/2583083002. Make sure that calling
these methods doesn't take effect when the renderer is foregrounded.

BUG=674784

Review-Url: https://codereview.chromium.org/2583193003
Cr-Commit-Position: refs/heads/master@{#439774}

third_party/WebKit/Source/platform/scheduler/renderer/renderer_scheduler_impl_unittest.cc

@@ -2285,6 +2285,14 @@ TEST_F(RendererSchedulerImplTest, SuspendRenderer) {
   RunUntilIdle();
   EXPECT_THAT(run_order,
               testing::ElementsAre(std::string("L1"), std::string("T1")));
+
+  run_order.clear();
+  PostTestTasks(&run_order, "D2 T2");
+  // The renderer is foregrounded. Suspending doesn't take effect.
+  scheduler_->SuspendRenderer();
+  RunUntilIdle();
+  EXPECT_THAT(run_order,
+              testing::ElementsAre(std::string("D2"), std::string("T2")));
 }
 
 TEST_F(RendererSchedulerImplTest, ResumeRenderer) {
@@ -2336,6 +2344,14 @@ TEST_F(RendererSchedulerImplTest, ResumeRenderer) {
   RunUntilIdle();
   EXPECT_THAT(run_order,
               testing::ElementsAre(std::string("D3"), std::string("T3")));
+
+  run_order.clear();
+  PostTestTasks(&run_order, "D4 T4");
+  // The renderer is foregrounded. Resuming doesn't take effect.
+  scheduler_->ResumeRenderer();
+  RunUntilIdle();
+  EXPECT_THAT(run_order,
+              testing::ElementsAre(std::string("D4"), std::string("T4")));
 }
 
 TEST_F(RendererSchedulerImplTest, UseCaseToString) {