[ExpandablePaymentHandler] Half height set to 50%

Before:
Half height is the bottom-sheet default 75%
(BottomSheet#HALF_HEIGHT_RATIO).

After:
Half height is customized to 50%.

Change:
Implement BottomSheetContent#getHalfHeightRatio.

Bug: 1060676

Change-Id: Ib586d4cbc22721b4ecb3b81413dcd3a42bd7fc9a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2098264Reviewed-by: Sahel Sharify <sahel@chromium.org>
Commit-Queue: Liquan (Max) Gu <maxlg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#749499}

chrome/android/java/src/org/chromium/chrome/browser/payments/handler/PaymentHandlerMediator.java

@@ -29,6 +29,7 @@ import org.chromium.ui.modelutil.PropertyModel;
         implements BottomSheetObserver, PaymentHandlerToolbarObserver, View.OnLayoutChangeListener {
     // The value is picked in order to allow users to see the tab behind this UI.
     /* package */ static final float FULL_HEIGHT_RATIO = 0.9f;
+    /* package */ static final float HALF_HEIGHT_RATIO = 0.5f;
 
     private final PropertyModel mModel;
     // Whenever invoked, invoked outside of the WebContentsObserver callbacks.

chrome/android/java/src/org/chromium/chrome/browser/payments/handler/PaymentHandlerView.java

@@ -83,6 +83,11 @@ import org.chromium.content_public.browser.WebContents;
         return PaymentHandlerMediator.FULL_HEIGHT_RATIO;
     }
 
+    @Override
+    public float getHalfHeightRatio() {
+        return PaymentHandlerMediator.HALF_HEIGHT_RATIO;
+    }
+
     @Override
     public boolean hasCustomScrimLifecycle() {
         return true;