Add support for setting TrackStart on solid color layers.

cc/animation/scrollbar_animation_controller_linear_fade_unittest.cc

Index: cc/animation/scrollbar_animation_controller_linear_fade_unittest.cc
diff --git a/cc/animation/scrollbar_animation_controller_linear_fade_unittest.cc b/cc/animation/scrollbar_animation_controller_linear_fade_unittest.cc
index 05e6155bd5036228b198bb4f0cd9e211a7f4f6ae..ea4b6e1c511f31fc55b3c086321e9ae151ccaf49 100644
--- a/cc/animation/scrollbar_animation_controller_linear_fade_unittest.cc
+++ b/cc/animation/scrollbar_animation_controller_linear_fade_unittest.cc
@@ -21,6 +21,7 @@ class ScrollbarAnimationControllerLinearFadeTest : public testing::Test {
  protected:
   virtual void SetUp() {
     const int kThumbThickness = 10;
+    const int kTrackStart = 0;
     const bool kIsLeftSideVerticalScrollbar = false;
     const bool kIsOverlayScrollbar = true;  // Allow opacity animations.
 
@@ -31,6 +32,7 @@ class ScrollbarAnimationControllerLinearFadeTest : public testing::Test {
                                              2,
                                              HORIZONTAL,
                                              kThumbThickness,
+                                             kTrackStart,
                                              kIsLeftSideVerticalScrollbar,
                                              kIsOverlayScrollbar);
     clip_layer_ = LayerImpl::Create(host_impl_.active_tree(), 3);