app_list: Improve visual feedback for invalid touch scroll.

- Reduce col padding for invalid transition to 15px and use a 50px for first
  column;
- Fix a problem that invalid transition gets reset when touch scroll is more
  than 100%;

BUG=none.
TEST=Verify icon moves less when attempting touch scroll to an invalid page.  Also invalid move is not abruptly reset in the middle while dragging the touch.

R=sky@chromium.org


Review URL: https://chromiumcodereview.appspot.com/10832255

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@151174 0039d316-1c4b-4281-b951-d872f2087c98

ui/app_list/apps_grid_view.cc

@@ -25,7 +25,11 @@ const int kPreferredTileWidth = 88;
 const int kPreferredTileHeight = 98;
 
 // Max extra column padding space in pixels for invalid page transition.
-const int kMaxExtraColPaddingForInvalidTransition = 80;
+const int kMaxExtraColPaddingForInvalidTransition = 15;
+
+// Extra column padding space in pixels of first column for invalid page
+// transition.
+const int kBaseExtraColPaddingForInvalidTransition = 50;
 
 }  // namespace
 
@@ -129,6 +133,8 @@ void AppsGridView::Layout() {
   const int transition_offset = is_valid ?
       transition.progress * page_width * dir :
       transition.progress * kMaxExtraColPaddingForInvalidTransition * dir;
+  const int base_transition_offset = is_valid ? 0 :
+      transition.progress * kBaseExtraColPaddingForInvalidTransition * dir;
 
   const int first_visible_index = current_page * tiles_per_page();
   const int last_visible_index = (current_page + 1) * tiles_per_page() - 1;
@@ -149,10 +155,11 @@ void AppsGridView::Layout() {
         x_offset += transition_offset;
     } else {
       const int col = i % cols_;
+      x_offset += base_transition_offset;
       if (transition_offset > 0)
-        x_offset += transition_offset * (col + 1);
+        x_offset += transition_offset * col;
       else
-        x_offset += transition_offset * (cols_ - col);
+        x_offset += transition_offset * (cols_ - col - 1);
     }
 
     gfx::Rect adjusted_slot(tile_slot);

ui/app_list/pagination_model.cc

@@ -114,9 +114,10 @@ void PaginationModel::UpdateScroll(double delta) {
   if (progress < 0) {
     clear_transition();
   } else if (progress > 1) {
-    if (is_valid_page(transition_.target_page))
+    if (is_valid_page(transition_.target_page)) {
       SelectPage(transition_.target_page, false);
       clear_transition();
+    }
   } else {
     transition_.progress = progress;
     NotifyTransitionChanged();