[NewTabPage] Refine fakebox scrolling transition on tablets.

- Add the tab strip height factor into the transition equation to make sure the
transition is anchored to the top of the tab.
- Override ntp_search_box_transition_length to make the transition take longer
on tablets.

BUG=625145

Review-Url: https://codereview.chromium.org/2345673002
Cr-Commit-Position: refs/heads/master@{#419137}

chrome/android/java/res/values-sw600dp/dimens.xml

@@ -34,6 +34,7 @@
 
     <!-- NTP dimensions -->
     <dimen name="ntp_logo_height">180dp</dimen>
+    <dimen name="ntp_search_box_transition_length">60dp</dimen>
 
     <!-- Recent tabs page -->
     <dimen name="recent_tabs_visible_separator_padding">28dp</dimen>

chrome/android/java/src/org/chromium/chrome/browser/ntp/NewTabPageView.java

@@ -490,10 +490,13 @@ public class NewTabPageView extends FrameLayout
         final int scrollY = getVerticalScroll();
         final float transitionLength =
                 getResources().getDimension(R.dimen.ntp_search_box_transition_length);
+        // Tab strip height is zero on phones, nonzero on tablets.
+        int tabStripHeight = getResources().getDimensionPixelSize(R.dimen.tab_strip_height);
 
-        // |scrollY - searchBoxTop| gives the distance the search bar is from the top of the screen.
-        return MathUtils.clamp(
-                (scrollY - searchBoxTop + transitionLength) / transitionLength, 0f, 1f);
+        // |scrollY - searchBoxTop + tabStripHeight| gives the distance the search bar is from the
+        // top of the tab.
+        return MathUtils.clamp((scrollY - searchBoxTop + transitionLength + tabStripHeight)
+                / transitionLength, 0f, 1f);
     }
 
     private ViewGroup getWrapperView() {