Tidy up null checking against WebContents

WebContentsUserData-backed objects requires its WebContents instance from
CVC be non-null, which causes numerous null checking statments. This CL
examines callsites to the methods that contains accesses to those
objects, adds null-checking statements if missing, and removes it
if redundant.

Some observations the changes are based on:

- private native method doesn't need null check; WebContents is
    certainly valid at that point.
- CVC.destroy() itself or calls from it (before it nulls out WebContents)
    doesn't need null check since WebContent is valid up to that point.

Added null check:
   ... since clusterfuzz results warn that these need it:
    - setTouchScrollInProgress
    - destroyPastePopup

   ... by moving it over from the 2 callsites:
    - updateTextSelectionUI (onAttachedToWindow, onDetachedFromWindow)

Removed null check as callsites already have null checking/assert,
      or assure WebContents is not null:
 - hidePopupsAndClearSelection (WebContentObserver.resetPopupsAndInput,
                                onFocusChanged, showSelectPopup)
 - hidePopupsAndPreserveSelection (destroy, onHide, updateTextSelectionUI,
                                   onFocusChanged, onRotationChanged)
 - hidePopups (above 2)
 - onAttachedToWindow, onDetachedFromWindow: moved to updateTextSelectionUI
 - onRotationChanged: consolidated null checks

Inlined one-liner restoreSelectionPopupsIfNecessary into callsites
 to eliminate the concern on null check on it (much clearer when inlined).

Bug: 810179
Change-Id: I55aab2b1f7917a9af4522a1bcf8d3e7d9b172f2a
Reviewed-on: https://chromium-review.googlesource.com/907770
Commit-Queue: Jinsuk Kim <jinsukkim@chromium.org>
Reviewed-by: Bo <boliu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#536016}

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

@@ -527,7 +527,7 @@ public class ContentViewCoreImpl
         assert mWebContents != null;
         mWebContents.onShow();
         getWebContentsAccessibility().refreshState();
-        restoreSelectionPopupsIfNecessary();
+        getSelectionPopupController().restoreSelectionPopupsIfNecessary();
     }
 
     @Override
@@ -543,34 +543,24 @@ public class ContentViewCoreImpl
     }
 
     private void hidePopupsAndClearSelection() {
-        if (mWebContents != null) {
-            getSelectionPopupController().destroyActionModeAndUnselect();
-            mWebContents.dismissTextHandles();
-        }
+        getSelectionPopupController().destroyActionModeAndUnselect();
+        mWebContents.dismissTextHandles();
         hidePopups();
     }
 
     @CalledByNative
     private void hidePopupsAndPreserveSelection() {
-        if (mWebContents != null) {
-            getSelectionPopupController().destroyActionModeAndKeepSelection();
-        }
+        getSelectionPopupController().destroyActionModeAndKeepSelection();
         hidePopups();
     }
 
     private void hidePopups() {
-        if (mWebContents != null) {
-            destroyPastePopup();
-            getTapDisambiguator().hidePopup(false);
-            getTextSuggestionHost().hidePopups();
-        }
+        destroyPastePopup();
+        getTapDisambiguator().hidePopup(false);
+        getTextSuggestionHost().hidePopups();
         hideSelectPopupWithCancelMessage();
     }
 
-    private void restoreSelectionPopupsIfNecessary() {
-        getSelectionPopupController().restoreSelectionPopupsIfNecessary();
-    }
-
     private void resetGestureDetection() {
         if (mNativeContentViewCore == 0) return;
         nativeResetGestureDetection(mNativeContentViewCore);
@@ -587,18 +577,18 @@ public class ContentViewCoreImpl
         mAttachedToWindow = true;
         for (WindowEventObserver observer : mWindowEventObservers) observer.onAttachedToWindow();
         addDisplayAndroidObserverIfNeeded();
-        if (mWebContents != null) {
-            updateTextSelectionUI(true);
-        }
+        updateTextSelectionUI(true);
         GamepadList.onAttachedToWindow(mContext);
         mSystemCaptioningBridge.addListener(this);
     }
 
     @Override
     public void updateTextSelectionUI(boolean focused) {
+        // TODO(jinsukkim): Replace all the null checks against mWebContents to assert stmt.
+        if (mWebContents == null) return;
         setTextHandlesTemporarilyHidden(!focused);
         if (focused) {
-            restoreSelectionPopupsIfNecessary();
+            getSelectionPopupController().restoreSelectionPopupsIfNecessary();
         } else {
             hidePopupsAndPreserveSelection();
         }
@@ -613,14 +603,12 @@ public class ContentViewCoreImpl
         removeDisplayAndroidObserver();
         GamepadList.onDetachedFromWindow();
 
-        if (mWebContents != null) {
-            // WebView uses PopupWindows for handle rendering, which may remain
-            // unintentionally visible even after the WebView has been detached.
-            // Override the handle visibility explicitly to address this, but
-            // preserve the underlying selection for detachment cases like screen
-            // locking and app switching.
-            updateTextSelectionUI(false);
-        }
+        // WebView uses PopupWindows for handle rendering, which may remain
+        // unintentionally visible even after the WebView has been detached.
+        // Override the handle visibility explicitly to address this, but
+        // preserve the underlying selection for detachment cases like screen
+        // locking and app switching.
+        updateTextSelectionUI(false);
         mSystemCaptioningBridge.removeListener(this);
     }
 
@@ -688,7 +676,7 @@ public class ContentViewCoreImpl
                 gainFocus && !getSelectionPopupController().isFocusedNodeEditable();
 
         if (gainFocus) {
-            restoreSelectionPopupsIfNecessary();
+            getSelectionPopupController().restoreSelectionPopupsIfNecessary();
         } else {
             cancelRequestToScrollFocusedEditableNodeIntoView();
             if (mPreserveSelectionOnNextLossOfFocus) {
@@ -1113,14 +1101,14 @@ public class ContentViewCoreImpl
         // ActionMode#invalidate() won't be able to re-layout the floating
         // action mode menu items according to the new rotation. So Chrome
         // has to re-create the action mode.
-        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M
-                && getSelectionPopupController().isActionModeValid()) {
-            hidePopupsAndPreserveSelection();
-            if (mWebContents != null) {
+        if (mWebContents != null) {
+            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M
+                    && getSelectionPopupController().isActionModeValid()) {
+                hidePopupsAndPreserveSelection();
                 getSelectionPopupController().showActionModeOrClearOnFailure();
             }
+            getTextSuggestionHost().hidePopups();
         }
-        if (mWebContents != null) getTextSuggestionHost().hidePopups();
 
         int rotationDegrees = 0;
         switch (rotation) {