Android: Fix NPE at ContentViewCoreImpl.onRotationChanged

Avoids calling methods on null object in ContentViewCoreImpl.
onRotationChanged by adding null checks.

Bug: 824156
Change-Id: I5af9eda71b61e06dc0e55f5eb211504d6dd04bd1
Reviewed-on: https://chromium-review.googlesource.com/981333Reviewed-by: Bo <boliu@chromium.org>
Commit-Queue: Jinsuk Kim <jinsukkim@chromium.org>
Cr-Commit-Position: refs/heads/master@{#546028}

content/public/android/java/src/org/chromium/content/browser/ContentViewCoreImpl.java

@@ -679,12 +679,14 @@ public class ContentViewCoreImpl implements ContentViewCore, DisplayAndroidObser
         // action mode menu items according to the new rotation. So Chrome
         // has to re-create the action mode.
         if (mWebContents != null) {
-            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M
-                    && getSelectionPopupController().isActionModeValid()) {
+            SelectionPopupControllerImpl controller = getSelectionPopupController();
+            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M && controller != null
+                    && controller.isActionModeValid()) {
                 hidePopupsAndPreserveSelection();
-                getSelectionPopupController().showActionModeOrClearOnFailure();
+                controller.showActionModeOrClearOnFailure();
             }
-            getTextSuggestionHost().hidePopups();
+            TextSuggestionHost host = getTextSuggestionHost();
+            if (host != null) host.hidePopups();
         }
 
         int rotationDegrees = 0;