Android: Fix a crash in Preview Tab

Preview Tab based on ThinWebView/BottomSheet is designed to reuse
the WebContents until the sheet is closed. But it was actually being
recreated for every new url due to how OverlayPanelContent works.

When preview tab displays an interstitial page with security state
change, the access to WebContents is made while it is in the destroyed
state, hence the reported crash occurred. This CL adds a new public
method in OverlayPanelContent so it has a way to reuse the WebContents.

Bug: 1030616
Change-Id: If9ed28dfefd83720ccd08fc6ef9fd6ffce92aa3c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2006836Reviewed-by: Donn Denman <donnd@chromium.org>
Commit-Queue: Jinsuk Kim <jinsukkim@chromium.org>
Cr-Commit-Position: refs/heads/master@{#733060}

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

@@ -268,12 +268,20 @@ public class OverlayPanelContent {
         }
     }
 
+    /**
+     * Whether we should reuse any existing WebContents instead of deleting and recreating.
+     * @param reuse {@code true} if we want to reuse the WebContents.
+     */
+    public void setReuseWebContents(boolean reuse) {
+        mShouldReuseWebContents = reuse;
+    }
+
     /**
      * Call this when a loadUrl request has failed to notify the panel that the WebContents can
      * be reused.  See crbug.com/682953 for details.
      */
     void onLoadUrlFailed() {
-        mShouldReuseWebContents = true;
+        setReuseWebContents(true);
     }
 
     /**

chrome/android/java/src/org/chromium/chrome/browser/compositor/bottombar/ephemeraltab/EphemeralTabCoordinator.java

@@ -139,6 +139,7 @@ public class EphemeralTabCoordinator implements View.OnLayoutChangeListener {
                     new PageLoadProgressObserver(), mActivity, mIsIncognito,
                     mActivity.getResources().getDimensionPixelSize(
                             R.dimen.toolbar_height_no_shadow));
+            mPanelContent.setReuseWebContents(true);
         }
         return mPanelContent;
     }