Make TranslateTransformOperation::X/Y return const Length&

Also eliminate a few copies in TranslateTransformOperation::Blend.

Change-Id: Icb390e3da70e2c3b651c34758f8e0fefa7bb4484
Reviewed-on: https://chromium-review.googlesource.com/970821Reviewed-by: Stephen Chenney <schenney@chromium.org>
Commit-Queue: Fredrik Söderquist <fs@opera.com>
Cr-Commit-Position: refs/heads/master@{#544377}

third_party/WebKit/Source/platform/transforms/TranslateTransformOperation.cpp

@@ -40,10 +40,9 @@ scoped_refptr<TransformOperation> TranslateTransformOperation::Blend(
         blink::Blend(z_, 0., progress), type_);
   }
 
-  const TranslateTransformOperation* from_op =
-      static_cast<const TranslateTransformOperation*>(from);
-  Length from_x = from_op ? from_op->x_ : zero_length;
-  Length from_y = from_op ? from_op->y_ : zero_length;
+  const auto* from_op = ToTranslateTransformOperation(from);
+  const Length& from_x = from_op ? from_op->x_ : zero_length;
+  const Length& from_y = from_op ? from_op->y_ : zero_length;
   double from_z = from_op ? from_op->z_ : 0;
   return TranslateTransformOperation::Create(
       x_.Blend(from_x, progress, kValueRangeAll),

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

@@ -63,8 +63,8 @@ class PLATFORM_EXPORT TranslateTransformOperation final
     return FloatValueForLength(y_, border_box_size.Height());
   }
 
-  Length X() const { return x_; }
-  Length Y() const { return y_; }
+  const Length& X() const { return x_; }
+  const Length& Y() const { return y_; }
   double Z() const { return z_; }
 
   void Apply(TransformationMatrix& transform,