Fix matrix3d transform under page zoom

third_party/WebKit/Source/platform/transforms/TransformationMatrix.h

Index: third_party/WebKit/Source/platform/transforms/TransformationMatrix.h
diff --git a/third_party/WebKit/Source/platform/transforms/TransformationMatrix.h b/third_party/WebKit/Source/platform/transforms/TransformationMatrix.h
index f9ae7d853bdd323278b4909a6db8639a0afe2669..f2bc7d9785f98169614cbf0bc219b1dd653b091d 100644
--- a/third_party/WebKit/Source/platform/transforms/TransformationMatrix.h
+++ b/third_party/WebKit/Source/platform/transforms/TransformationMatrix.h
@@ -337,6 +337,16 @@ class PLATFORM_EXPORT TransformationMatrix {
     return applyTransformOrigin(origin.x(), origin.y(), origin.z());
   }
 
+  // Changes the transform to:
+  //
+  //     scale3d(z, z, z) * mat * scale3d(1/z, 1/z, 1/z)
+  //
+  // Useful for mapping zoomed points to their zoomed transformed result:
+  //
+  //     new_mat * (scale3d(z, z, z) * x) == scale3d(z, z, z) * (mat * x)
+  //

[alancutter (OOO until 2018), 2016/11/10 06:50:03]

Nice comment! I'd even put this in the description, it's very succinct and
clear.

+  TransformationMatrix& zoom(double zoomFactor);
+
   bool isInvertible() const;
 
   // This method returns the identity matrix if it is not invertible.