[Merge to M60] Keep the wrapper of FetchEvent alive while waiting for the preload response.

[Merge to M60] Keep the wrapper of FetchEvent alive while waiting for the preload response.

This CL uses ActiveScriptWrappable and implements HasPendingActivity() to keep the wrapper of FetchEvent alive while waiting for the preload response.

FetchEvents are already kept alive by ServiceWorkerGlobalScopeProxy's |pending_preload_fetch_events_| until the preload response.
But the resolver function is not called in the current implementation if GC happens. (https://crbug.com/728013#c28)
That is because if the wrapper of FetchEvent are GCed, ScriptPromiseProperty can't call the resolver.

BUG=728013
Review-Url: https://codereview.chromium.org/2922863002
Cr-Original-Commit-Position: refs/heads/master@{#476977}
Review-Url: https://codereview.chromium.org/2922283002 .
Cr-Commit-Position: refs/branch-heads/3112@{#174}
Cr-Branched-From: b6460e24cf59f429d69de255538d0fc7a425ccf9-refs/heads/master@{#474897}
Committed: https://chromium.googlesource.com/chromium/src/+/50e7718fc9bc2d63c3c8a69de2a25864b970ba0b

[horo, 2017-06-06 00:15:17]

Description was changed from

==========
[Merge to M60] Keep the wrapper of FetchEvent alive while waiting for the
preload response.

This CL uses ActiveScriptWrappable and implements HasPendingActivity() to keep
the wrapper of FetchEvent alive while waiting for the preload response.

FetchEvents are already kept alive by ServiceWorkerGlobalScopeProxy's
|pending_preload_fetch_events_| until the preload response.
But the resolver function is not called in the current implementation if GC
happens. (https://crbug.com/728013#c28)
That is because if the wrapper of FetchEvent are GCed, ScriptPromiseProperty
can't call the resolver.

BUG=728013

Review-Url: https://codereview.chromium.org/2922863002
Cr-Commit-Position: refs/heads/master@{#476977}
(cherry picked from commit 7f1ac9b18fed816431798435d68d8ee90668d392)
==========

to

==========
[Merge to M60] Keep the wrapper of FetchEvent alive while waiting for the
preload response.

This CL uses ActiveScriptWrappable and implements HasPendingActivity() to keep
the wrapper of FetchEvent alive while waiting for the preload response.

FetchEvents are already kept alive by ServiceWorkerGlobalScopeProxy's
|pending_preload_fetch_events_| until the preload response.
But the resolver function is not called in the current implementation if GC
happens. (https://crbug.com/728013#c28)
That is because if the wrapper of FetchEvent are GCed, ScriptPromiseProperty
can't call the resolver.

BUG=728013

Review-Url: https://codereview.chromium.org/2922863002
Cr-Original-Commit-Position: refs/heads/master@{#476977}
Review-Url: https://codereview.chromium.org/2922283002 .
Cr-Commit-Position: refs/branch-heads/3112@{#174}
Cr-Branched-From:
b6460e24cf59f429d69de255538d0fc7a425ccf9-refs/heads/master@{#474897}
Committed:
https://chromium.googlesource.com/chromium/src/+/50e7718fc9bc2d63c3c8a69de2a2...
==========

[horo, 2017-06-06 00:15:20]

Committed patchset #1 (id:1) manually as
50e7718fc9bc2d63c3c8a69de2a25864b970ba0b.