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. To use this object, first
+// create an instance of BooleanObserver and call |setObservedObject:keyPath:|.
+// After an expected change in the value of |keyPath|, ask for |lastValue| and
+// compare to the expected value.
+@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.

[Eugene But (OOO till 7-30), 2017/05/23 19:49:33]

"has not been observed" and "observed NO" are not distinguishable. Should we use
NSNumber instead?

[michaeldo, 2017/05/24 15:02:34]

Done.

+@property(nonatomic, readonly) BOOL lastValue;
+
+// The |keyPath| of |object| being observed.
+@property(nonatomic, nullable, readonly) NSString* keyPath;
+
+// The current |object| being observed.
+@property(nonatomic, nullable, 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.
+// If |object| is null and |self.object| is nonnull, |self.object| will stop
+// being observed. If |object| is nonnull, |keyPath| must be nonnull.
+- (void)setObservedObject:(nullable NSObject*)object
+                  keyPath:(nullable NSString*)keyPath;
+
+@end
+
+#endif  // IOS_WEB_VIEW_TEST_BOOLEAN_OBSERVER_H_