Implement OverlayPanels as SceneOverlays

chrome/android/java/src/org/chromium/chrome/browser/compositor/bottombar/OverlayPanelBase.java

Index: chrome/android/java/src/org/chromium/chrome/browser/compositor/bottombar/OverlayPanelBase.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/compositor/bottombar/OverlayPanelBase.java b/chrome/android/java/src/org/chromium/chrome/browser/compositor/bottombar/OverlayPanelBase.java
index c0037279b1c4b24fe6d770aa47bd624bd42e5c2e..5f97fb3c4b32b2845e1de378e04b8cc7adbf50ec 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/compositor/bottombar/OverlayPanelBase.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/compositor/bottombar/OverlayPanelBase.java
@@ -281,7 +281,8 @@ abstract class OverlayPanelBase {
     }
 
     /**
-     * @return Whether the Overlay Panel is opened. That is, whether it is EXPANDED or MAXIMIZED.
+     * @return Whether the Overlay Panel is opened. That is, whether the current height is greater
+     * than the peeking height.
      */
     public boolean isPanelOpened() {
         return mHeight > mBarHeightPeeking;
@@ -496,8 +497,8 @@ abstract class OverlayPanelBase {
     // Base Page states
     // --------------------------------------------------------------------------------------------
 
-    private float mBasePageY;
-    private float mBasePageBrightness;
+    private float mBasePageY = 0.0f;
+    private float mBasePageBrightness = 1.0f;
 
     /**
      * @return The vertical offset of the base page.