Make 2D canvas disable gpu acceleration when getImageData is called

third_party/WebKit/Source/platform/graphics/Canvas2DLayerBridge.cpp

Index: third_party/WebKit/Source/platform/graphics/Canvas2DLayerBridge.cpp
diff --git a/third_party/WebKit/Source/platform/graphics/Canvas2DLayerBridge.cpp b/third_party/WebKit/Source/platform/graphics/Canvas2DLayerBridge.cpp
index e2fb6df93a917264297cce6c1b1204cf811f47b3..7b137e74b09249b174512d4deba11b9ea0ccef8b 100644
--- a/third_party/WebKit/Source/platform/graphics/Canvas2DLayerBridge.cpp
+++ b/third_party/WebKit/Source/platform/graphics/Canvas2DLayerBridge.cpp
@@ -464,22 +464,50 @@ void Canvas2DLayerBridge::reportSurfaceCreationFailure()
     }
 }
 
+void Canvas2DLayerBridge::disableAcceleration()
+{
+    DCHECK(m_layer);
+    bool surfaceIsAccelerated;
+    RefPtr<SkSurface> newSurface = createSkSurface(nullptr, m_size, m_msaaSampleCount, m_opacityMode, &surfaceIsAccelerated);
+    if (newSurface) {
+        DCHECK(!surfaceIsAccelerated);
+        flush();
+        SkPaint copyPaint;
+        copyPaint.setXfermodeMode(SkXfermode::kSrc_Mode);
+        m_surface->draw(newSurface->getCanvas(), 0, 0, &copyPaint); // GPU readback here
+        m_accelerationMode = DisableAcceleration; // Acceleration gets permanently disabled
+        GraphicsLayer::unregisterContentsLayer(m_layer->layer());
+        m_layer->clearTexture();
+        m_layer->layer()->removeFromParent();
+        m_layer.reset();
+        m_surface = newSurface;
+        if (m_imageBuffer)
+            m_imageBuffer->didDisableAcceleration();
+    }
+}
+
 SkSurface* Canvas2DLayerBridge::getOrCreateSurface(AccelerationHint hint)
 {
-    if (m_surface)
+    if (m_surface) {
+        // Note: in layout tests, canvas2dFixedRenderingMode is set to true to inhibit
+        // mode switching so that we continue to get test coverage for GPU acceleration
+        // despite the use of getImageData in tests
+        if (hint == ForceNoAcceleration && m_layer && !RuntimeEnabledFeatures::canvas2dFixedRenderingModeEnabled())
+            disableAcceleration();
         return m_surface.get();
+    }
 
     if (m_layer && !isHibernating() && hint == PreferAcceleration) {
         return nullptr; // re-creation will happen through restore()
     }
 
     bool wantAcceleration = shouldAccelerate(hint);
-    bool surfaceIsAccelerated;
     if (CANVAS2D_BACKGROUND_RENDER_SWITCH_TO_CPU && isHidden() && wantAcceleration) {
         wantAcceleration = false;
         m_softwareRenderingWhileHidden = true;
     }
 
+    bool surfaceIsAccelerated;
     m_surface = createSkSurface(wantAcceleration ? m_contextProvider->grContext() : nullptr, m_size, m_msaaSampleCount, m_opacityMode, &surfaceIsAccelerated);
 
     if (!m_surface)