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

cc/layer_tree_host.cc

Index: cc/layer_tree_host.cc
diff --git a/cc/layer_tree_host.cc b/cc/layer_tree_host.cc
index 91276deb8ad5bcb005ec733ce1713e3e0f543d63..059741eb31dbea716be01a0af06a729a8cd27e02 100644
--- a/cc/layer_tree_host.cc
+++ b/cc/layer_tree_host.cc
@@ -796,7 +796,13 @@ gfx::PointF LayerTreeHost::adjustEventPointForPinchZoom(const gfx::PointF& zoome
 
     // Scale to screen space before applying implTransform inverse.
     gfx::PointF zoomedScreenspacePoint = gfx::ScalePoint(zoomedViewportPoint, deviceScaleFactor());
-    gfx::Transform inverseImplTransform = MathUtil::inverse(m_implTransform);
+
+    // Note carefully, this remains an identity matrix if m_implTransform is uninvertible.
+    // TODO: see if there is something more reasonable we can do if m_implTransform really is uninvertible.
+    //       or perhaps we can just DCHECK that m_implTransform should be invertible?
+    gfx::Transform inverseImplTransform(gfx::Transform::kSkipInitialization);
+    if (!m_implTransform.GetInverse(&inverseImplTransform))
+        inverseImplTransform.MakeIdentity();
 
     bool wasClipped = false;
     gfx::PointF unzoomedScreenspacePoint = MathUtil::projectPoint(inverseImplTransform, zoomedScreenspacePoint, wasClipped);