Don't restart the ImageQualityController timer unless it is already half over.

third_party/WebKit/Source/core/layout/ImageQualityControllerTest.cpp

Index: third_party/WebKit/Source/core/layout/ImageQualityControllerTest.cpp
diff --git a/third_party/WebKit/Source/core/layout/ImageQualityControllerTest.cpp b/third_party/WebKit/Source/core/layout/ImageQualityControllerTest.cpp
index c9e585a53181716764b22aa3db8880a33067883f..a54ba3c47ced2536b32918117a09561eb4122361 100644
--- a/third_party/WebKit/Source/core/layout/ImageQualityControllerTest.cpp
+++ b/third_party/WebKit/Source/core/layout/ImageQualityControllerTest.cpp
@@ -112,6 +112,7 @@ class MockTimer : public Timer<ImageQualityController> {
 public:
     MockTimer(ImageQualityController* o, TimerFiredFunction f)
     : Timer<ImageQualityController>(o, f)
+    , started(false)

[Xianzhu, 2016/04/22 19:39:17]

Nit: Indent 4 more spaces.

     {
     }
 
@@ -120,6 +121,14 @@ public:
         this->Timer<ImageQualityController>::fired();
         stop();
     }
+
+    void startOneShot(double interval, const WebTraceLocation& caller) override

[Xianzhu, 2016/04/22 18:14:59]

Can you use Timer::isActive() and Timer::cancel() instead of making this method
virtual?

[chrishtr, 2016/04/22 18:30:35]

I'm not sure how to do that. Are you suggesting cancelling the timer in the test
and checking whether it was re-started? That won't work because
the code checks for it being inactive before the other logic.

I think I could use nextFireInterval() and mock out time...

[Xianzhu, 2016/04/22 19:39:17]

I see Timer::cancel() would affect what we want to test.

Would this work:
- Add double Timer::nextFireTime() const { return m_nextFireTime; }
- Check if nextFireTime() changed after calling shouldPaintAtLowQuality().

[Xianzhu, 2016/04/22 19:49:51]

Just noticed that you would have to mock the time. I think this is worth doing
to avoid changing Timer::startOneShot().

+    {
+        Timer<ImageQualityController>::startOneShot(interval, caller);
+        started = true;
+    }
+
+    bool started;
 };
 
 TEST_F(ImageQualityControllerTest, LowQualityFilterForResizingImage)
@@ -203,6 +212,31 @@ TEST_F(ImageQualityControllerTest, DontKickTheAnimationTimerWhenPaintingAtTheSam
     EXPECT_FALSE(mockTimer->isActive());
 }
 
+TEST_F(ImageQualityControllerTest, DontRestartTimerUnlessAdvanced)
+{
+    MockTimer* mockTimer = new MockTimer(controller(), &ImageQualityController::highQualityRepaintTimerFired);
+    controller()->setTimer(mockTimer);
+    setBodyInnerHTML("<img src='myimage'></img>");
+    LayoutImage* img = toLayoutImage(document().body()->firstChild()->layoutObject());
+
+    RefPtr<TestImageLowQuality> testImage = adoptRef(new TestImageLowQuality);
+
+    // Paint once. This will kick off a timer to see if we resize it during that timer's execution.
+    EXPECT_FALSE(mockTimer->started);
+
+    EXPECT_EQ(false, controller()->shouldPaintAtLowQuality(*img, testImage.get(), testImage.get(), LayoutSize(2, 2), 0.1));
+    EXPECT_TRUE(mockTimer->started);
+
+    // Go into low-quality mode now that the size changed.
+    mockTimer->started = false;
+    EXPECT_EQ(true, controller()->shouldPaintAtLowQuality(*img, testImage.get(), testImage.get(), LayoutSize(3, 3), 0.1 + ImageQualityController::cTimerRestartThreshold / 2.0));
+    EXPECT_FALSE(mockTimer->started);
+
+    // This animation is far enough in the future to make the timer restart, since it is half over.
+    EXPECT_EQ(true, controller()->shouldPaintAtLowQuality(*img, testImage.get(), testImage.get(), LayoutSize(4, 4), 0.1 + ImageQualityController::cTimerRestartThreshold + 0.01));
+    EXPECT_TRUE(mockTimer->started);
+}
+
 #endif
 
 } // namespace blink