cc: Adding testing for commits triggering NeedsBeginFrame.

This CL does two things;

 * Makes the commit requested test explicitly check that
   a commit only occurs during the impl frame.

 * Adds check for the case where commit is requested by
   can't draw.

This test was extracted from my original CL at
https://codereview.chromium.org/792803008/

BUG=346230

Review URL: https://codereview.chromium.org/1055673005

Cr-Commit-Position: refs/heads/master@{#324215}

cc/scheduler/scheduler_state_machine_unittest.cc

@@ -248,6 +248,35 @@ TEST(SchedulerStateMachineTest, TestNextActionBeginsMainFrameIfNeeded) {
 
     EXPECT_TRUE(state.BeginFrameNeeded());
 
+    // Expect nothing to happen until after OnBeginImplFrame.
+    EXPECT_COMMIT_STATE(SchedulerStateMachine::COMMIT_STATE_IDLE);
+    EXPECT_IMPL_FRAME_STATE(SchedulerStateMachine::BEGIN_IMPL_FRAME_STATE_IDLE);
+    EXPECT_ACTION(SchedulerStateMachine::ACTION_NONE);
+
+    state.OnBeginImplFrame();
+    EXPECT_ACTION_UPDATE_STATE(
+        SchedulerStateMachine::ACTION_SEND_BEGIN_MAIN_FRAME);
+  }
+
+  // If commit requested and can't draw, still begin a main frame.
+  {
+    StateMachine state(default_scheduler_settings);
+    state.SetCommitState(SchedulerStateMachine::COMMIT_STATE_IDLE);
+    state.SetCanStart();
+    state.UpdateState(state.NextAction());
+    state.CreateAndInitializeOutputSurfaceWithActivatedCommit();
+    state.SetNeedsRedraw(false);
+    state.SetVisible(true);
+    state.SetNeedsCommit();
+    state.SetCanDraw(false);
+
+    EXPECT_TRUE(state.BeginFrameNeeded());
+
+    // Expect nothing to happen until after OnBeginImplFrame.
+    EXPECT_COMMIT_STATE(SchedulerStateMachine::COMMIT_STATE_IDLE);
+    EXPECT_IMPL_FRAME_STATE(SchedulerStateMachine::BEGIN_IMPL_FRAME_STATE_IDLE);
+    EXPECT_ACTION(SchedulerStateMachine::ACTION_NONE);
+
     state.OnBeginImplFrame();
     EXPECT_ACTION_UPDATE_STATE(
         SchedulerStateMachine::ACTION_SEND_BEGIN_MAIN_FRAME);