[Contextual Search] Improve testing & add regressions tests

chrome/android/java/src/org/chromium/chrome/browser/compositor/bottombar/contextualsearch/ContextualSearchPanelBase.java

Index: chrome/android/java/src/org/chromium/chrome/browser/compositor/bottombar/contextualsearch/ContextualSearchPanelBase.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/compositor/bottombar/contextualsearch/ContextualSearchPanelBase.java b/chrome/android/java/src/org/chromium/chrome/browser/compositor/bottombar/contextualsearch/ContextualSearchPanelBase.java
index 390bf363b09a702d5aa4cb5fe3e0d078111e4f76..7af52d2a42ee05294961db130a369d3d0a15bd84 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/compositor/bottombar/contextualsearch/ContextualSearchPanelBase.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/compositor/bottombar/contextualsearch/ContextualSearchPanelBase.java
@@ -810,8 +810,6 @@ abstract class ContextualSearchPanelBase implements ContextualSearchPromoHost {
      * @param reason The reason for a change in the panel's state.
      */
     public void setPanelState(PanelState state, StateChangeReason reason) {
-        mPanelState = state;
-
         if (state == PanelState.CLOSED) {
             mIsShowing = false;
             onClosed(reason);
@@ -819,6 +817,12 @@ abstract class ContextualSearchPanelBase implements ContextualSearchPromoHost {
                 || (state == PanelState.MAXIMIZED && !isFullscreenSizePanel())) {
             showPromoViewAtYPosition(getPromoYPx());
         }
+
+        // We should only set the state at the end of this method, in oder to make sure that
+        // all callbacks will be fired before changing the state of the Panel. This prevents
+        // some flakiness on tests since they rely on changes of state to determine when a
+        // particular action has been completed.
+        mPanelState = state;
     }
 
     /**