Fix more issues with scrim and bottom sheet

This patch removes a check that causes the scrim to remain visable
after the bottom sheet is closed. The check in question blocked offset
change events if the bottom sheet is closed, but in certain cases like
when the sheet doesn't animate, the sheets state is closed before any
offset events occur.

This patch also adds a BottomSheetObserver when the sheet is opened
that controls the opacity of the scrim and removes it when the sheet
is closed.

Bug: 842902,842765
Change-Id: Ic70532cefa0ddcafc06d0a2b3a5b6e28639ff24e
Reviewed-on: https://chromium-review.googlesource.com/1058437
Commit-Queue: Matthew Jones <mdjones@chromium.org>
Reviewed-by: Theresa <twellington@chromium.org>
Cr-Commit-Position: refs/heads/master@{#558814}

chrome/android/java/src/org/chromium/chrome/browser/widget/bottomsheet/BottomSheetController.java

@@ -164,6 +164,14 @@ public class BottomSheetController implements ApplicationStatus.ActivityStateLis
             }
         });
 
+        final BottomSheetObserver scrimAlphaSheetObserver = new EmptyBottomSheetObserver() {
+            @Override
+            public void onTransitionPeekToHalf(float transitionFraction) {
+                fadingBackgroundView.setViewAlpha(transitionFraction);
+            }
+        };
+
+        // Handles attaching the observer that controls the placement and visibility of the scrim.
         mBottomSheet.addObserver(new EmptyBottomSheetObserver() {
             /**
              * The index of the scrim in the view hierarchy prior to being moved for the bottom
@@ -171,14 +179,9 @@ public class BottomSheetController implements ApplicationStatus.ActivityStateLis
              */
             private int mOriginalScrimIndexInParent;
 
-            @Override
-            public void onTransitionPeekToHalf(float transitionFraction) {
-                if (!mBottomSheet.isSheetOpen()) return;
-                fadingBackgroundView.setViewAlpha(transitionFraction);
-            }
-
             @Override
             public void onSheetOpened(@BottomSheet.StateChangeReason int reason) {
+                mBottomSheet.addObserver(scrimAlphaSheetObserver);
                 mOriginalScrimIndexInParent = UiUtils.getChildIndexInParent(fadingBackgroundView);
                 ViewGroup parent = (ViewGroup) fadingBackgroundView.getParent();
                 UiUtils.removeViewFromParent(fadingBackgroundView);
@@ -187,10 +190,12 @@ public class BottomSheetController implements ApplicationStatus.ActivityStateLis
 
             @Override
             public void onSheetClosed(@BottomSheet.StateChangeReason int reason) {
+                mBottomSheet.removeObserver(scrimAlphaSheetObserver);
                 assert mOriginalScrimIndexInParent >= 0;
                 ViewGroup parent = (ViewGroup) fadingBackgroundView.getParent();
                 UiUtils.removeViewFromParent(fadingBackgroundView);
                 parent.addView(fadingBackgroundView, mOriginalScrimIndexInParent);
+                fadingBackgroundView.setViewAlpha(0);
             }
 
             @Override