Flatten webview hierarchy

[kiftio]

What changes are you making?

We still have a BaseWebView.. This made sense with CheckoutWebView and FallbackWebView for graceful degradation. Now we don't have FallbackWebView we should flatten that down

---
BaseWebView has been removed as an abstract base class. All of its functionality — WebView configuration, touch gesture handling, user agent suffix generation, back-press handling, navigation error handling, and removeFromParent — has been consolidated directly into CheckoutWebView.

The ECP_LOG_TAG and SCROLL_UP_DIRECTION constants previously nested inside BaseWebView are now top-level package-level declarations, and references to BaseWebView.ECP_LOG_TAG across CheckoutProtocol, EmbeddedCheckoutProtocolBridge, and WebMessageTransport have been updated accordingly.

CheckoutBottomSheetScrollHandoff and test helpers that previously referenced BaseWebView now reference CheckoutWebView directly. Test subclasses (ScrollableBaseWebView, GestureTestWebView) have been updated to extend CheckoutWebView instead, removing the need to override getListener().

How to test

1. Build the Android library and confirm there are no compilation errors.
2. Run the existing unit test suites (CheckoutWebViewTest, CheckoutBottomSheetTest) and verify all tests pass.
3. Launch the CheckoutKitAndroidDemo sample app and complete a checkout flow end-to-end, verifying that progress indication, gesture handling (scroll handoff with the bottom sheet), back navigation, and error handling all behave correctly.
4. Confirm that preloading a checkout URL and then presenting it works as expected.

---

Before you merge

Important

• I've added tests to support my implementation
• I have read and agree with the Contribution Guidelines
• I have read and agree with the Code of Conduct
• I've updated the relevant platform README (platforms/swift/README.md and/or platforms/android/README.md)

---

Releasing a new Swift version?

• I have bumped the version in ShopifyCheckoutKit.podspec
• I have bumped the version in platforms/swift/Sources/ShopifyCheckoutKit/ShopifyCheckoutKit.swift
• I have updated the SwiftPM/CocoaPods version snippets in platforms/swift/README.md (major version only)

Releasing a new Embedded Checkout Protocol version?

• I have bumped embeddedCheckoutProtocolAndroid in platforms/android/gradle/libs.versions.toml
• I have updated protocol/languages/kotlin/embedded-checkout-protocol/api/embedded-checkout-protocol.api if the public API changed

Releasing a new Android version?

• I have bumped checkoutKitAndroid in platforms/android/gradle/libs.versions.toml
• I have updated the Gradle/Maven version snippets in platforms/android/README.md

Tip

See the Contributing documentation for the full release process per platform.

[kiftio]

• Flatten webview hierarchy #497 👈 (View in Graphite)
• main

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[github-actions]

React Native — Coverage Report

Lines	Statements	Branches	Functions
	91.85% (327/356)	87.98% (183/208)	100% (86/86)

[github-actions]

Package Size

Platform	Artifact	Base	Head	Delta
Android	release AAR	246.5 KiB	245.6 KiB	-897 B

Android file breakdown

File	Base	Head	Delta
classes.jar	260.7 KiB	259.9 KiB	-826 B
res/layout/checkout_view_content.xml	2.2 KiB	2.2 KiB	0 B
res/layout/checkout_sheet_content.xml	2.0 KiB	2.0 KiB	0 B
res/values/values.xml	1.2 KiB	1.2 KiB	0 B
R.txt	1.1 KiB	1.1 KiB	0 B
proguard.txt	798 B	798 B	0 B
AndroidManifest.xml	578 B	578 B	0 B
res/drawable/close.xml	431 B	431 B	0 B
res/menu/checkout_menu.xml	354 B	354 B	0 B
META-INF/com/android/build/gradle/aar-metadata.properties	157 B	157 B	0 B

Measured from the PR base SHA and PR head SHA. The file breakdown shows uncompressed sizes within each package artifact, so individual files do not sum to the compressed artifact total. This comment reports package artifact sizes only; it is not a final app binary-size report.

[bitrise]

Install this build

Open Tophat, select your target device, then click Install. Links open on the Mac running Tophat.

SDK	Install
Kotlin	Install with Tophat

Checkout Kit E2E results

Status	Suite	Target	Platform	OS version tag	Device
✅	tests/shared/launch-smoke.yaml	kotlin	android	latest	Google Pixel 9 Android 17.0