Add unittest to test CWVWebView.

ios/web_view/test/boolean_observer.h

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef IOS_WEB_VIEW_TEST_BOOLEAN_OBSERVER_H_
+#define IOS_WEB_VIEW_TEST_BOOLEAN_OBSERVER_H_
+
+#import <Foundation/Foundation.h>
+
+// Class to observe a boolean KVO compliant property.

[Eugene But (OOO till 7-30), 2017/05/19 18:39:48]

Could you please explain in the comments how to use this class.

[michaeldo, 2017/05/23 16:20:51]

Done.

+@interface BooleanObserver : NSObject
+
+// The last value of performing |keyPath| on |object| after being notified of a
+// KVO value change. NO if a change has not been observed.
+@property(nonatomic, readonly) BOOL lastValue;

[Eugene But (OOO till 7-30), 2017/05/19 18:39:48]

Should we implement more generic class that can observe all types?

[michaeldo, 2017/05/23 16:20:51]

Yes, but I will do this in a followup CL as part of supporting NSString KVO
observing (to test CWVWebView title changes). In that CL we can determine the
best way to abstract this into a more generic class or split it into a few
specific observer classes.

+
+// The |keyPath| of |object| being observed.
+@property(nonatomic, readonly) NSString* keyPath;
+
+// The current |object| being observed.
+@property(nonatomic, readonly, weak) NSObject* object;
+
+// Sets the |object| and |keyPath| to observe. Performing |keyPath| on |object|
+// must return a BOOL value and |keyPath| must be KVO compliant.
+- (void)setObservedObject:(NSObject*)object keyPath:(NSString*)keyPath;

[Eugene But (OOO till 7-30), 2017/05/19 18:39:48]

Do you want to use nullability annotation and explain that object can be null
but keyPath can't?

[michaeldo, 2017/05/23 16:20:51]

Added. PTAL. I think |keyPath| can be null if object is allowed to be null.
otherwise we should require nonnull for both params. (we could expose separate
method to stop observing an object if necessary.)

+
+@end
+
+#endif  // IOS_WEB_VIEW_TEST_BOOLEAN_OBSERVER_H_