Hookup android_webview scroll offset delegation to Java side.

android_webview/java/src/org/chromium/android_webview/AwScrollOffsetManager.java

Index: android_webview/java/src/org/chromium/android_webview/AwScrollOffsetManager.java
diff --git a/android_webview/java/src/org/chromium/android_webview/AwScrollOffsetManager.java b/android_webview/java/src/org/chromium/android_webview/AwScrollOffsetManager.java
new file mode 100644
index 0000000000000000000000000000000000000000..c23b37bb4b5ed4b0b5892c692d354029a41f5bb4
--- /dev/null
+++ b/android_webview/java/src/org/chromium/android_webview/AwScrollOffsetManager.java
@@ -0,0 +1,54 @@
+// Copyright 2012 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.
+
+package org.chromium.android_webview;
+
+import org.chromium.base.CalledByNative;
+
+class AwScrollOffsetManager {
+    public interface Delegate {
+        // Returns whether the update succeeded
+        boolean scrollContainerViewTo(int xPix, int yPix);
+        void scrollNativeTo(int xCss, int yCss);
+        int getContainerViewScrollXPix();
+        int getContainerViewScrollYPix();
+    }
+
+    final Delegate mDelegate;
+    final double mDIPScale;
+    boolean mIgnoreContainerViewScrollChanges;
+    int mNativeScrollXPix;
+    int mNativeScrollYPix;
+
+    public AwScrollOffsetManager(Delegate delegate, double dipScale) {
+        mDelegate = delegate;
+        mDIPScale = dipScale;
+    }
+
+    public void scrollContainerViewTo(int xCss, int yCss) {

[joth, 2013/06/18 03:19:50]

don't CSS pixels normally travel in a float?

[mkosiba (inactive), 2013/06/18 18:09:25]

yes, they should.

+        mNativeScrollXPix = (int) (xCss * mDIPScale);
+        mNativeScrollYPix = (int) (yCss * mDIPScale);

[joth, 2013/06/18 03:19:50]

maybe it's not difference either way, but I was hoping to keep CSS pixels as an
internal concept to lower (native) layers and keep java in framework units. Is
there specific need for this to be css here? I guess this maybe water under the
bridge as ContentViewCore is already boshing values about in CSS units?

[mkosiba (inactive), 2013/06/18 18:09:25]

I don't think there is a really compelling reason. The alternative was to push
the DIP scale into the in_process_view_renderer.cc, so I thought this would be
simpler, but I can see the benefits of sticking to the framework pixel units in
Java.

[joth, 2013/06/19 05:34:45]

I think in_process_view_renderer.cc will need to know these conversions
whatever: see  https://code.google.com/p/chromium/issues/detail?id=224003 and
also my TODO in InProcessViewRenderer::RenderSW
https://code.google.com/p/chromium/codesearch#chromium/src/android_webview/br...

so I if it does work out just as well to do this conversion there too, I'd
rather keep that in the one place -- all else being equal etc etc.

+
+        if (!mDelegate.scrollContainerViewTo(mNativeScrollXPix, mNativeScrollYPix)) {
+            scrollNativeTo(mDelegate.getContainerViewScrollXPix(),
+                    mDelegate.getContainerViewScrollYPix());

[joth, 2013/06/18 03:19:50]

the logic in this class is verging on so simple it is adding more mental
overhead having the extra class and abstractions than it helps. Writing tests
for it as part of AwContents would be a mess though, it's true

[mkosiba (inactive), 2013/06/18 18:09:25]

the main reason I opted to make this a separate class is that I expect I'll have
to add some fun code here in the future (to correctly support pinch-zoomable
wrap-content webviews we'll have to ensure the correct scroll offset ourselves
:/)

+        }
+    }
+
+    public void onContainerViewScrollChanged(int xPix, int yPix) {
+        scrollNativeTo(xPix, yPix);
+    }
+
+    private void scrollNativeTo(int xPix, int yPix) {
+        if (xPix == mNativeScrollXPix && yPix == mNativeScrollYPix)
+            return;
+
+        mNativeScrollXPix = xPix;
+        mNativeScrollYPix = yPix;
+
+        int xCss = (int) (xPix / mDIPScale);
+        int yCss = (int) (yPix / mDIPScale);
+        mDelegate.scrollNativeTo(xCss, yCss);
+    }
+}