[Android] Disallow null stubs on DeferredViewStubInflationProvider

Currently, the DeferredViewStubInflationProvider will accept null as
view stub and try to inflate the non-existent stub much later.

To prevent this deferred NullPointerException, assert that used stubs
are never null. Fix the usage that uncovered that issue.

Bug: 876215
Change-Id: I51deb6aaa1ac3d3283e6794c0cae37c536b43aa5
Reviewed-on: https://chromium-review.googlesource.com/1210783Reviewed-by: Theresa <twellington@chromium.org>
Commit-Queue: Friedrich Horschig [CEST] <fhorschig@chromium.org>
Cr-Commit-Position: refs/heads/master@{#589487}

chrome/android/java/src/org/chromium/chrome/browser/ChromeActivity.java

@@ -1379,10 +1379,13 @@ public abstract class ChromeActivity extends AsyncInitializationActivity
             setStatusBarColor(null, mBaseStatusBarColor);
         }, coordinator);
 
-        mManualFillingController.initialize(getWindowAndroid(),
-                new DeferredViewStubInflationProvider<>(findViewById(R.id.keyboard_accessory_stub)),
-                new DeferredViewStubInflationProvider<>(
-                        findViewById(R.id.keyboard_accessory_sheet_stub)));
+        ViewStub accessoryBarStub = findViewById(R.id.keyboard_accessory_stub);
+        ViewStub accessorySheetStub = findViewById(R.id.keyboard_accessory_sheet_stub);
+        if (accessoryBarStub != null && accessorySheetStub != null) {
+            mManualFillingController.initialize(getWindowAndroid(),
+                    new DeferredViewStubInflationProvider<>(accessoryBarStub),
+                    new DeferredViewStubInflationProvider<>(accessorySheetStub));
+        }
 
         // Create after native initialization so subclasses that override this method have a chance
         // to setup.

ui/android/java/src/org/chromium/ui/DeferredViewStubInflationProvider.java

@@ -21,6 +21,7 @@ public class DeferredViewStubInflationProvider<T extends View> implements ViewPr
 
     @SuppressWarnings("unchecked")
     public DeferredViewStubInflationProvider(ViewStub viewStub) {
+        assert viewStub != null : "ViewStub to inflate may not be null!";
         mViewStub = viewStub;
         mViewStub.setOnInflateListener((stub, inflated) -> { mViewPromise.fulfill((T) inflated); });
     }