Migrate from MathUtil::inverse() to gfx::Transform::GetInverse()

cc/layer_tree_host_impl.cc

Index: cc/layer_tree_host_impl.cc
diff --git a/cc/layer_tree_host_impl.cc b/cc/layer_tree_host_impl.cc
index 408e8417971f300adfce4cb83a855ddaf80153bc..dd6d1f57d7d8d7a0665a007cbac47f0541969566 100644
--- a/cc/layer_tree_host_impl.cc
+++ b/cc/layer_tree_host_impl.cc
@@ -481,8 +481,6 @@ static void appendQuadsToFillScreen(RenderPass* targetRenderPass, LayerImpl* roo
     // doesn't have any bounds and so can't generate this itself.
     // FIXME: Make the gutter quads generated by the solid color layer (make it smarter about generating quads to fill unoccluded areas).
 
-    DCHECK(rootLayer->screenSpaceTransform().IsInvertible());
-
     gfx::Rect rootTargetRect = rootLayer->renderSurface()->contentRect();
     float opacity = 1;
     SharedQuadState* sharedQuadState = quadCuller.useSharedQuadState(SharedQuadState::Create());
@@ -494,10 +492,16 @@ static void appendQuadsToFillScreen(RenderPass* targetRenderPass, LayerImpl* roo
                             opacity);
 
     AppendQuadsData appendQuadsData;
-    gfx::Transform transformToLayerSpace = MathUtil::inverse(rootLayer->screenSpaceTransform());
+
+    // Even though we always expect the screen space transform to be invertible if we
+    // reach this code, we still try to handle the uninvertible case for Release mode.
+    DCHECK(rootLayer->screenSpaceTransform().IsInvertible());
+    gfx::Transform transformToLayerSpace(gfx::Transform::kSkipInitialization);
+    if (!rootLayer->screenSpaceTransform().GetInverse(&transformToLayerSpace))
+        transformToLayerSpace.MakeIdentity();
     for (Region::Iterator fillRects(fillRegion); fillRects.has_rect(); fillRects.next()) {
         // The root layer transform is composed of translations and scales only,
-        // no perspective, so mapping is sufficient.
+        // no perspective, so mapping is sufficient (as opposed to projecting).
         gfx::Rect layerRect = MathUtil::mapClippedRect(transformToLayerSpace, fillRects.rect());
         // Skip the quad culler and just append the quads directly to avoid
         // occlusion checks.
@@ -1264,9 +1268,12 @@ InputHandlerClient::ScrollStatus LayerTreeHostImpl::scrollBegin(gfx::Point viewp
 static gfx::Vector2dF scrollLayerWithViewportSpaceDelta(PinchZoomViewport* viewport, LayerImpl& layerImpl, float scaleFromViewportToScreenSpace, gfx::PointF viewportPoint, gfx::Vector2dF viewportDelta)
 {
     // Layers with non-invertible screen space transforms should not have passed the scroll hit
-    // test in the first place.
+    // test in the first place. Even though we always expect the screen space transform to be invertible
+    // if we reach this code, we still try to handle the uninvertible case for Release mode.
     DCHECK(layerImpl.screenSpaceTransform().IsInvertible());
-    gfx::Transform inverseScreenSpaceTransform = MathUtil::inverse(layerImpl.screenSpaceTransform());
+    gfx::Transform inverseScreenSpaceTransform(gfx::Transform::kSkipInitialization);
+    if (!layerImpl.screenSpaceTransform().GetInverse(&inverseScreenSpaceTransform))
+        inverseScreenSpaceTransform.MakeIdentity();
 
     gfx::PointF screenSpacePoint = gfx::ScalePoint(viewportPoint, scaleFromViewportToScreenSpace);