[Android WebView] Defer scrolls until provided a valid content size

With the synchronous compositor, valid scroll offsets may be improperly 
clamped before the frame swap message provides the view a valid content size.
Allow for deferred application of the view container scroll offset until a valid
content size is received by AwScrollOffsetManager.

BUG=293770

Review URL: https://chromiumcodereview.appspot.com/23480086

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@223780 0039d316-1c4b-4281-b951-d872f2087c98

2 files changed, 71 insertions, 0 deletions

diff --git a/android_webview/java/src/org/chromium/android_webview/AwScrollOffsetManager.java b/android_webview/java/src/org/chromium/android_webview/AwScrollOffsetManager.java
index 1eca5aa..e849520 100644
--- a/android_webview/java/src/org/chromium/android_webview/AwScrollOffsetManager.java
+++ b/android_webview/java/src/org/chromium/android_webview/AwScrollOffsetManager.java
@@ -69,6 +69,12 @@ public class AwScrollOffsetManager {
     private int mDeferredNativeScrollX;
     private int mDeferredNativeScrollY;
 
+    // Whether (and to what value) to update the container view scroll offset after we've received
+    // a valid content size.
+    private boolean mApplyDeferredContainerScrollOnValidContentSize;
+    private int mDeferredContainerScrollX;
+    private int mDeferredContainerScrollY;
+
     // The velocity of the last recorded fling,
     private int mLastFlingVelocityX;
     private int mLastFlingVelocityY;
@@ -117,6 +123,12 @@ public class AwScrollOffsetManager {
     public void setContentSize(int width, int height) {
         mContentWidth = width;
         mContentHeight = height;
+
+        if (mApplyDeferredContainerScrollOnValidContentSize &&
+                mContentWidth != 0 && mContentHeight != 0) {
+            mApplyDeferredContainerScrollOnValidContentSize = false;
+            scrollContainerViewTo(mDeferredContainerScrollX, mDeferredContainerScrollY);
+        }
     }
 
     // Called when the physical size of the view changes.
@@ -144,6 +156,14 @@ public class AwScrollOffsetManager {
 
     // Called by the native side to attempt to scroll the container view.
     public void scrollContainerViewTo(int x, int y) {
+        if (mContentWidth == 0 && mContentHeight == 0) {
+            mApplyDeferredContainerScrollOnValidContentSize = true;
+            mDeferredContainerScrollX = x;
+            mDeferredContainerScrollY = y;
+            return;
+        }
+        mApplyDeferredContainerScrollOnValidContentSize = false;
+
         mNativeScrollX = x;
         mNativeScrollY = y;
 
@@ -235,6 +255,9 @@ public class AwScrollOffsetManager {
         if (x == mNativeScrollX && y == mNativeScrollY)
             return;
 
+        // Updating the native scroll will override any pending scroll originally sent from native.
+        mApplyDeferredContainerScrollOnValidContentSize = false;
+
         // The scrollNativeTo call should be a simple store, so it's OK to assume it always
         // succeeds.
         mNativeScrollX = x;
diff --git a/android_webview/javatests/src/org/chromium/android_webview/test/AwScrollOffsetManagerTest.java b/android_webview/javatests/src/org/chromium/android_webview/test/AwScrollOffsetManagerTest.java
index b692820..176c451 100644
--- a/android_webview/javatests/src/org/chromium/android_webview/test/AwScrollOffsetManagerTest.java
+++ b/android_webview/javatests/src/org/chromium/android_webview/test/AwScrollOffsetManagerTest.java
@@ -214,6 +214,54 @@ public class AwScrollOffsetManagerTest extends InstrumentationTestCase {
         assertEquals(0, delegate.getNativeScrollY());
     }
 
+
+    @SmallTest
+    @Feature({"AndroidWebView"})
+    public void testScrollDeferredOnInvalidContentSize() {
+        TestScrollOffsetManagerDelegate delegate = new TestScrollOffsetManagerDelegate();
+        OverScroller scroller = new OverScroller(getInstrumentation().getContext());
+        AwScrollOffsetManager offsetManager = new AwScrollOffsetManager(delegate, scroller);
+
+        offsetManager.setContentSize(0, 0);
+        offsetManager.setContainerViewSize(VIEW_WIDTH, VIEW_HEIGHT);
+
+        final int firstScrollX = MAX_HORIZONTAL_OFFSET + 10;
+        final int firstScrollY = MAX_VERTICAL_OFFSET + 11;
+        int expectedCallCount = delegate.getOverScrollCallCount();
+        offsetManager.scrollContainerViewTo(firstScrollX, firstScrollY);
+        assertEquals(expectedCallCount, delegate.getOverScrollCallCount());
+        assertEquals(0, delegate.getOverScrollDeltaX() + delegate.getScrollX());
+        assertEquals(0, delegate.getOverScrollDeltaY() + delegate.getScrollY());
+
+        // Repeated scrolls will also be deferred, overwriting any previous deferred scroll offset.
+        final int secondScrollX = MAX_HORIZONTAL_OFFSET;
+        final int secondScrollY = MAX_VERTICAL_OFFSET;
+        offsetManager.scrollContainerViewTo(secondScrollX, secondScrollY);
+        assertEquals(expectedCallCount, delegate.getOverScrollCallCount());
+        assertEquals(0, delegate.getOverScrollDeltaX() + delegate.getScrollX());
+        assertEquals(0, delegate.getOverScrollDeltaY() + delegate.getScrollY());
+
+        // Setting a valid size will release the deferred container scroll offset.
+        expectedCallCount++;
+        offsetManager.setContentSize(CONTENT_WIDTH, CONTENT_HEIGHT);
+        assertEquals(expectedCallCount, delegate.getOverScrollCallCount());
+        assertEquals(secondScrollX, delegate.getOverScrollDeltaX() + delegate.getScrollX());
+        assertEquals(secondScrollY, delegate.getOverScrollDeltaY() + delegate.getScrollY());
+        offsetManager.onContainerViewOverScrolled(secondScrollX, secondScrollY, false, false);
+
+        assertEquals(secondScrollX, delegate.getOverScrollDeltaX());
+        assertEquals(secondScrollY, delegate.getOverScrollDeltaY());
+        assertEquals(MAX_HORIZONTAL_OFFSET, delegate.getScrollX());
+        assertEquals(MAX_VERTICAL_OFFSET, delegate.getScrollY());
+
+        // Subsequently setting valid content sizes should not release another scroll update.
+        offsetManager.setContentSize(CONTENT_WIDTH + 10, CONTENT_HEIGHT + 10);
+        assertEquals(expectedCallCount, delegate.getOverScrollCallCount());
+        offsetManager.setContentSize(CONTENT_WIDTH, CONTENT_HEIGHT);
+        assertEquals(expectedCallCount, delegate.getOverScrollCallCount());
+    }
+
+
     @SmallTest
     @Feature({"AndroidWebView"})
     public void testDelegateCanOverrideScroll() {