Add exceptions to help diagnose null sheet content

This patch throws exceptions for cases that shouldn't be happening
when using the bottom sheet. These will hopefully help track down an
issue where the sheet is visible with null content.

Bug: 1126872
Change-Id: I65789df1a569674d19610f41e50b45e21edb1136
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2403902Reviewed-by: Theresa  <twellington@chromium.org>
Commit-Queue: Matthew Jones <mdjones@chromium.org>
Cr-Commit-Position: refs/heads/master@{#805904}

components/browser_ui/android/bottomsheet/internal/java/src/org/chromium/components/browser_ui/bottomsheet/BottomSheetControllerImpl.java

@@ -377,6 +377,10 @@ class BottomSheetControllerImpl implements ManagedBottomSheetController {
 
     @Override
     public boolean requestShowContent(BottomSheetContent content, boolean animate) {
+        if (content == null) {
+            throw new RuntimeException("Attempting to show null content in the sheet!");
+        }
+
         if (mBottomSheet == null) mSheetInitializer.run();
 
         // If already showing the requested content, do nothing.
@@ -456,6 +460,10 @@ class BottomSheetControllerImpl implements ManagedBottomSheetController {
      * @param animate Whether the sheet should animate opened.
      */
     private void showNextContent(boolean animate) {
+        if (mBottomSheet.getSheetState() != SheetState.HIDDEN) {
+            throw new RuntimeException("Showing next content before sheet is hidden!");
+        }
+
         if (mContentQueue.isEmpty()) {
             mBottomSheet.showContent(null);
             return;