Bug 142205

Summary: REGRESSION(r180902): It broke scrolling in some cases. See bug 142202 for details. (Requested by bdash on #webkit).
Product: WebKit Reporter: WebKit Commit Bot <commit-queue>
Component: New BugsAssignee: WebKit Commit Bot <commit-queue>
Status: RESOLVED FIXED    
Severity: Normal CC: bfulgham, mrowe, simon.fraser
Priority: P2    
Version: 528+ (Nightly build)   
Hardware: Unspecified   
OS: Unspecified   
Bug Depends on:    
Bug Blocks: 142102    
Attachments:
Description Flags
ROLLOUT of r180902 none

Description WebKit Commit Bot 2015-03-02 19:24:27 PST 
http://trac.webkit.org/changeset/180902 broke the build:
It broke scrolling in some cases. See bug 142202 for details. (Requested by bdash on #webkit).

This is an automatic bug report generated by webkitbot. If this bug
report was created because of a flaky test, please file a bug for the flaky
test (if we don't already have one on file) and dup this bug against that bug
so that we can track how often these flaky tests fail.
Comment 1 WebKit Commit Bot 2015-03-02 19:24:57 PST 
Created attachment 247737 [details]
ROLLOUT of r180902

Any committer can land this patch automatically by marking it commit-queue+.  The commit-queue will build and test the patch before landing to ensure that the rollout will be successful.  This process takes approximately 15 minutes.

If you would like to land the rollout faster, you can use the following command:

  webkit-patch land-attachment ATTACHMENT_ID

where ATTACHMENT_ID is the ID of this attachment.
Comment 2 Mark Rowe (bdash) 2015-03-02 19:26:23 PST 
*** Bug 142202 has been marked as a duplicate of this bug. ***
Comment 3 WebKit Commit Bot 2015-03-02 19:30:03 PST 
Comment on attachment 247737 [details]
ROLLOUT of r180902

Clearing flags on attachment: 247737

Committed r180915: <http://trac.webkit.org/changeset/180915>
Comment 4 WebKit Commit Bot 2015-03-02 19:30:07 PST 
All reviewed patches have been landed.  Closing bug.
Comment 5 Brent Fulgham 2015-03-03 15:56:45 PST 
This bug was caused by an error in my refactoring of ScrollingTreeScrollingNodeMac. The original "snapRubberbandTimer" implementation made sure to notify the scrollingTree that rubber banding was ended, and to reset the content size of the scrolling node. When I consolidated the stop timer methods, I lost this step.

This caused the scrolling thread's view of the scrollable area to no longer match the main thread. The scrolling thread then allowed the user to scroll down far past the end of the document.

Attempts to build a test that notices this problem are confounded by the fact that querying the DOM for the scroll area size returns the right information (even with this bug) because the main thread copy of the state is correct.