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 12ab72b4cfcdf649fc2f07e17828e546f3aa2134..6fab3f343771543645f84a1bd9cbda880584a8de 100644
--- a/cc/layer_tree_host.cc
+++ b/cc/layer_tree_host.cc
@@ -794,7 +794,12 @@ 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);
+
+    gfx::Transform inverseImplTransform(gfx::Transform::kSkipInitialization);
+    if (!m_implTransform.GetInverse(&inverseImplTransform)) {
+        // TODO(shawnsingh): Either we need to handle uninvertible transforms
+        // here, or DCHECK that the transform is invertible.

[danakj, 2013/01/04 21:56:07]

Thanks, I like how this makes current potential bugs really glaring.

+    }
 
     bool wasClipped = false;
     gfx::PointF unzoomedScreenspacePoint = MathUtil::projectPoint(inverseImplTransform, zoomedScreenspacePoint, wasClipped);