Add (back) assignment operator overloads over Persistent<> types.

Add (back) assignment operator overloads over Persistent<> types.

Overloads aren't inherited, so add the required delegating operator=
overload implementation for (CrossThread)(Weak)Persistent<> types.

Without these, an assignment like

  V :: Persistent<T>
  X :: RawPtr<T>

  V = X;

will be desugared & compiled as

  V = Persistent<T>(X);  // where "=" is the copy constructor.

i.e., introducing (and allocating) a temporary Persistent<> for the RHS.

(This assignment shows up when initializing a WebPrivatePtr<T> over a GCed
type T, for instance.)

R=haraken
BUG=420515
Committed: https://crrev.com/ca262b0755f50b738722c5857973a5535b7d1afe
git-svn-id: svn://svn.chromium.org/blink/trunk@202191 bbb929c8-8fbe-4397-9dbb-9b2b20218538

[sof, 2015-09-11 20:58:08]

sigbjornf@opera.com changed reviewers:
+ oilpan-reviews@chromium.org

[sof, 2015-09-11 20:58:08]

please take a look.

[haraken, 2015-09-12 03:31:18]

LGTM

[sof, 2015-09-12 05:41:40]

The CQ bit was checked by sigbjornf@opera.com

[commit-bot: I haz the power, 2015-09-12 05:41:50]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1335303002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1335303002/1

[commit-bot: I haz the power, 2015-09-12 11:14:35]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-09-12 11:14:36]

Try jobs failed on following builders:
  linux_chromium_gn_rel on tryserver.chromium.linux (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...)

[sof, 2015-09-12 14:39:45]

The CQ bit was checked by sigbjornf@opera.com

[commit-bot: I haz the power, 2015-09-12 14:39:51]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1335303002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1335303002/1

[sof, 2015-09-12 17:14:16]

The CQ bit was unchecked by sigbjornf@opera.com

[sof, 2015-09-12 17:26:17]

https://codereview.chromium.org/1335303002/diff/1/Source/platform/heap/Handle.h
File Source/platform/heap/Handle.h (right):

https://codereview.chromium.org/1335303002/diff/1/Source/platform/heap/Handle...
Source/platform/heap/Handle.h:299: template<typename U>
Cut&paste error - this one shouldn't be parameterized; will fix & pass along
again.

[sof, 2015-09-12 20:59:33]

The CQ bit was checked by sigbjornf@opera.com

[sof, 2015-09-12 20:59:33]

The patchset sent to the CQ was uploaded after l-g-t-m from haraken@chromium.org
Link to the patchset: https://codereview.chromium.org/1335303002/#ps20001
(title: "remove erroneous parameterization of operator=(std::nullptr_t)s")

[commit-bot: I haz the power, 2015-09-12 20:59:41]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1335303002/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1335303002/20001

[commit-bot: I haz the power, 2015-09-12 23:05:43]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-09-12 23:05:44]

Try jobs failed on following builders:
  win_chromium_x64_rel_ng on tryserver.chromium.win (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_x64_...)

[sof, 2015-09-13 05:42:09]

The CQ bit was checked by sigbjornf@opera.com

[commit-bot: I haz the power, 2015-09-13 05:42:17]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1335303002/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1335303002/20001

[commit-bot: I haz the power, 2015-09-13 11:15:36]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-09-13 11:15:37]

Try jobs failed on following builders:
  linux_chromium_gn_rel on tryserver.chromium.linux (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...)

[sof, 2015-09-13 11:40:43]

The CQ bit was checked by sigbjornf@opera.com

[commit-bot: I haz the power, 2015-09-13 11:40:48]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1335303002/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1335303002/20001

[commit-bot: I haz the power, 2015-09-13 14:43:16]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-09-13 14:43:16]

Try jobs failed on following builders:
  linux_chromium_clobber_rel_ng on tryserver.chromium.linux (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...)

[sof, 2015-09-13 14:48:31]

The CQ bit was checked by sigbjornf@opera.com

[commit-bot: I haz the power, 2015-09-13 14:48:42]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1335303002/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1335303002/20001

[commit-bot: I haz the power, 2015-09-13 20:49:17]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-09-13 20:49:19]

Try jobs failed on following builders:
  linux_chromium_clobber_rel_ng on tryserver.chromium.linux (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...)

[sof, 2015-09-14 05:11:11]

The CQ bit was checked by sigbjornf@opera.com

[commit-bot: I haz the power, 2015-09-14 05:11:19]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1335303002/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1335303002/20001

[commit-bot: I haz the power, 2015-09-14 05:34:32]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-09-14 05:34:33]

Try jobs failed on following builders:
  chromeos_daisy_chromium_compile_only_ng on tryserver.chromium.linux
(JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.linux/builders/chromeos_daisy_...)

[sof, 2015-09-14 06:51:44]

The CQ bit was checked by sigbjornf@opera.com

[commit-bot: I haz the power, 2015-09-14 06:51:51]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1335303002/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1335303002/20001

[commit-bot: I haz the power, 2015-09-14 08:20:41]

Committed patchset #2 (id:20001) as
https://src.chromium.org/viewvc/blink?view=rev&revision=202191

[commit-bot: I haz the power, 2015-09-23 12:30:49]

Patchset 2 (id:??) landed as
https://crrev.com/ca262b0755f50b738722c5857973a5535b7d1afe