ash: Add accelerator for snapping windows left/right.

ash/wm/workspace/snap_sizer.cc

Index: ash/wm/workspace/snap_sizer.cc
diff --git a/ash/wm/workspace/snap_sizer.cc b/ash/wm/workspace/snap_sizer.cc
index 158fa3a599a02ec7b860686a3d3d03c326850368..0816ff00acdbc40b6e6537745a97af9d6d5e9a86 100644
--- a/ash/wm/workspace/snap_sizer.cc
+++ b/ash/wm/workspace/snap_sizer.cc
@@ -66,6 +66,18 @@ void SnapSizer::Update(const gfx::Point& location) {
   time_last_update_ = base::TimeTicks::Now();
 }
 
+gfx::Rect SnapSizer::GetSnapBounds(const gfx::Rect& bounds) {
+  size_t current;
+  for (current = 0; current < arraysize(kPercents); ++current) {
+    gfx::Rect target = GetTargetBoundsForPercent(current);
+    if (target == bounds) {
+      ++current;
+      break;
+    }
+  }
+  return GetTargetBoundsForPercent(current % arraysize(kPercents));
+}
+
 int SnapSizer::CalculateIncrement(int x, int reference_x) const {
   if (AlongEdge(x))
     return 1;
@@ -94,12 +106,16 @@ void SnapSizer::ChangeBounds(int x, int delta) {
 }
 
 gfx::Rect SnapSizer::GetTargetBounds() const {
+  return GetTargetBoundsForPercent(percent_index_);
+}
+
+gfx::Rect SnapSizer::GetTargetBoundsForPercent(int percent_index) const {
   gfx::Rect work_area(ScreenAsh::GetUnmaximizedWorkAreaBounds(window_));
   int y = WindowResizer::AlignToGridRoundUp(work_area.y(), grid_size_);
   // We don't align to the bottom of the grid as the launcher may not
   // necessarily align to the grid (happens when auto-hidden).
   int max_y = work_area.bottom();
-  int width = static_cast<float>(work_area.width()) * kPercents[percent_index_];
+  int width = static_cast<float>(work_area.width()) * kPercents[percent_index];
   if (edge_ == LEFT_EDGE) {
     int x = WindowResizer::AlignToGridRoundUp(work_area.x(), grid_size_);
     int mid_x = WindowResizer::AlignToGridRoundUp(