android scroller: Stop fling earlier.

If the fling update is close to the final state, then stop the fling. The
threshold for this used to be 1e-5f, but change it to 1e-1f, since there
won't be any visual changes for subsequent fling-update steps.

BUG=none
R=jdduke@chromium.org

Review URL: https://codereview.chromium.org/606093002

Cr-Commit-Position: refs/heads/master@{#297198}

ui/gfx/android/scroller.cc

@@ -25,6 +25,10 @@ const float kInflexion = 0.35f;
 
 const float kEpsilon = 1e-5f;
 
+// Fling scroll is stopped when the scroll position is |kThresholdForFlingEnd|
+// pixels or closer from the end.
+const float kThresholdForFlingEnd = 0.1;
+
 bool ApproxEquals(float a, float b) {
   return std::abs(a - b) < kEpsilon;
 }
@@ -324,9 +328,10 @@ bool Scroller::ComputeScrollOffset(base::TimeTicks time) {
       curr_y_ = start_y_ + distance_coef * delta_y_;
       curr_y_ = Clamped(curr_y_, min_y_, max_y_);
 
-      if (ApproxEquals(curr_x_, final_x_) && ApproxEquals(curr_y_, final_y_)) {
+      float diff_x = std::abs(curr_x_ - final_x_);
+      float diff_y = std::abs(curr_y_ - final_y_);
+      if (diff_x < kThresholdForFlingEnd && diff_y < kThresholdForFlingEnd)
         finished_ = true;
-      }
     } break;
   }
 

ui/gfx/android/scroller_unittest.cc

@@ -14,8 +14,8 @@ const float kDefaultStartX = 7.f;
 const float kDefaultStartY = 25.f;
 const float kDefaultDeltaX = -20.f;
 const float kDefaultDeltaY = 73.f;
-const float kDefaultVelocityX = -35.f;
-const float kDefaultVelocityY = 22.f;
+const float kDefaultVelocityX = -350.f;
+const float kDefaultVelocityY = 220.f;
 const float kEpsilon = 1e-3f;
 
 Scroller::Config DefaultConfig() {

ui/gfx/gfx_tests.gyp

@@ -25,6 +25,7 @@
       ],
       'all_sources': [
         '<@(_common_sources)',
+        'android/scroller_unittest.cc',
         'animation/animation_container_unittest.cc',
         'animation/animation_unittest.cc',
         'animation/multi_animation_unittest.cc',