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

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

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/layout/ImageQualityController.h"
 
 #include "core/layout/LayoutImage.h"
 #include "core/layout/LayoutTestHelper.h"
 #include "platform/graphics/GraphicsContext.h"
 #include "platform/graphics/paint/PaintController.h"
@@ skipping 94 matching lines @@
 
     RefPtr<TestImageLowQuality> testImage = adoptRef(new TestImageLowQuality);
     EXPECT_EQ(InterpolationMedium, controller()->chooseInterpolationQuality(*img, testImage.get(), testImage.get(), LayoutSize(1, 1)));
 }
 
 class MockTimer : public Timer<ImageQualityController> {
     typedef void (ImageQualityController::*TimerFiredFunction)(Timer*);
 public:
     MockTimer(ImageQualityController* o, TimerFiredFunction f)
     : Timer<ImageQualityController>(o, f)
+    , started(false)

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

Nit: Indent 4 more spaces.

     {
     }
 
     void fire()
     {
         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)
 {
     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);
@@ skipping 63 matching lines @@
     EXPECT_EQ(InterpolationLow, controller()->chooseInterpolationQuality(*img, testImage.get(), testImage.get(), LayoutSize(4, 4)));
 
     mockTimer->stop();
     EXPECT_FALSE(mockTimer->isActive());
     // Painted at the same size, so even though timer is still executing, don't go to low quality.
     EXPECT_EQ(InterpolationLow, controller()->chooseInterpolationQuality(*img, testImage.get(), testImage.get(), LayoutSize(4, 4)));
     // Check that the timer was not kicked. It should not have been, since the image was painted at the same size as last time.
     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