Implement clearListener() method for PositionObserver to clear all registered listeners when Con

Implement clearListener() method for PositionObserver to
clear all registered listeners when ContentViewCore is destroyed.
    
PositionObserver listeners are not cleared and left as it is which will eventually not go for garbage collection.
Hence listeners should be cleared when ContentViewCore is destroyed.

BUG=None.

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=285244

[wajahat, 2014-07-21 14:35:49]

PTAL!

[Yaron, 2014-07-22 19:20:25]

https://codereview.chromium.org/407893003/diff/1/content/public/android/java/...
File
content/public/android/java/src/org/chromium/content/browser/ViewPositionObserver.java
(left):

https://codereview.chromium.org/407893003/diff/1/content/public/android/java/...
content/public/android/java/src/org/chromium/content/browser/ViewPositionObserver.java:64:
if (mListeners.contains(listener)) return;
This is different than what ObserverList is deisgned for. It ensures that you
can make modifications while iteratring over the list of observers, not that you
don't re-add an observer that's already present.

https://codereview.chromium.org/407893003/diff/1/content/public/android/java/...
File
content/public/android/java/src/org/chromium/content/browser/ViewPositionObserver.java
(right):

https://codereview.chromium.org/407893003/diff/1/content/public/android/java/...
content/public/android/java/src/org/chromium/content/browser/ViewPositionObserver.java:20:
private final ObserverList<Listener> mListeners;
Note that there is slightly more overhead to using ObserverList so it shouldn't
be used arbitrarily.

[wajahat, 2014-07-23 04:24:16]

Changes Incorporated as per comments.
PTAL!

https://codereview.chromium.org/407893003/diff/1/content/public/android/java/...
File
content/public/android/java/src/org/chromium/content/browser/ViewPositionObserver.java
(left):

https://codereview.chromium.org/407893003/diff/1/content/public/android/java/...
content/public/android/java/src/org/chromium/content/browser/ViewPositionObserver.java:64:
if (mListeners.contains(listener)) return;
On 2014/07/22 19:20:25, Yaron wrote:
> This is different than what ObserverList is deisgned for. It ensures that you
> can make modifications while iteratring over the list of observers, not that
you
> don't re-add an observer that's already present.

ok, reverting this change

https://codereview.chromium.org/407893003/diff/1/content/public/android/java/...
File
content/public/android/java/src/org/chromium/content/browser/ViewPositionObserver.java
(right):

https://codereview.chromium.org/407893003/diff/1/content/public/android/java/...
content/public/android/java/src/org/chromium/content/browser/ViewPositionObserver.java:20:
private final ObserverList<Listener> mListeners;
On 2014/07/22 19:20:25, Yaron wrote:
> Note that there is slightly more overhead to using ObserverList so it
shouldn't
> be used arbitrarily.

ok reverting this change

[Yaron, 2014-07-23 18:25:59]

lgtm

[wajahat, 2014-07-24 05:21:51]

The CQ bit was checked by wajahat.s@samsung.com

[commit-bot: I haz the power, 2014-07-24 05:24:12]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/wajahat.s@samsung.com/407893003/20001

[commit-bot: I haz the power, 2014-07-24 07:24:34]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  android_dbg_triggered_tests on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/android_dbg_triggered...)
  win8_chromium_rel on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/win8_chromium_rel/bui...)
  linux_gpu_triggered_tests on tryserver.chromium.gpu
(http://build.chromium.org/p/tryserver.chromium.gpu/builders/linux_gpu_trigger...)

[commit-bot: I haz the power, 2014-07-24 14:11:10]

Change committed as 285244