[Offline indicator v2] Fix regression in VTS and a11y tab switcher

Currently, the vertical and a11y tab switchers observe the browser
controls even if they aren't visible. This affects the rendering
performance for the tabs.

The fix is to add/remove the observer when the layout shows/hides.

Bug: 1105601
Change-Id: I60fd18fdeebf3d281ab95146a16c99ff8c5acde5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2300986Reviewed-by: Matthew Jones <mdjones@chromium.org>
Reviewed-by: Theresa  <twellington@chromium.org>
Commit-Queue: Sinan Sahin <sinansahin@google.com>
Cr-Commit-Position: refs/heads/master@{#789241}

chrome/android/java/src/org/chromium/chrome/browser/accessibility_tab_switcher/OverviewListLayout.java

@@ -58,7 +58,6 @@ public class OverviewListLayout extends Layout
                 adjustForFullscreen();
             }
         };
-        mBrowserControlsStateProvider.addObserver(mBrowserControlsObserver);
     }
 
     @Override
@@ -163,10 +162,14 @@ public class OverviewListLayout extends Layout
         mTabModelWrapper.setStateBasedOnModel();
 
         doneShowing();
+        mBrowserControlsStateProvider.addObserver(mBrowserControlsObserver);
+        adjustForFullscreen();
     }
 
     @Override
     public void startHiding(int nextId, boolean hintAtTabSelection) {
+        mBrowserControlsStateProvider.removeObserver(mBrowserControlsObserver);
+
         super.startHiding(nextId, hintAtTabSelection);
 
         doneHiding();

chrome/android/java/src/org/chromium/chrome/browser/compositor/layouts/phone/StackLayoutBase.java

@@ -404,6 +404,8 @@ public abstract class StackLayoutBase extends Layout {
             @Override
             public void onControlsOffsetChanged(int topOffset, int topControlsMinHeightOffset,
                     int bottomOffset, int bottomControlsMinHeightOffset, boolean needsAnimate) {
+                if (!isActive()) return;
+
                 notifySizeChanged(mWidth, mHeight, mOrientation);
             }
         };
@@ -952,6 +954,16 @@ public abstract class StackLayoutBase extends Layout {
         updateLayout(time, 0);
     }
 
+    @Override
+    public void doneShowing() {
+        super.doneShowing();
+
+        if (mBrowserControlsSupplier.get() != null) {
+            mBrowserControlsSupplier.get().addObserver(mBrowserControlsObserver);
+            notifySizeChanged(mWidth, mHeight, mOrientation);
+        }
+    }
+
     @Override
     public void notifySizeChanged(float width, float height, @Orientation int orientation) {
         mWidth = width;
@@ -1448,6 +1460,10 @@ public abstract class StackLayoutBase extends Layout {
 
     @Override
     public void startHiding(int nextTabId, boolean hintAtTabSelection) {
+        if (mBrowserControlsSupplier.get() != null) {
+            mBrowserControlsSupplier.get().removeObserver(mBrowserControlsObserver);
+        }
+
         super.startHiding(nextTabId, hintAtTabSelection);
 
         // Reset mIsActiveLayout here instead of in doneHiding() so if a user hits the tab switcher