Revert of FileWriter should not use deprecated {,un}setPendingActivity (https://codereview.chromium.org/383103002/)

Reason for revert:
Leaks started in:
file-metadata-after-write.html 
file-writer-abort-continue.html 
file-writer-abort-depth.html 
file-writer-abort.html 
file-writer-empty-blob.html 
file-writer-events.html 
file-writer-gc-blob.html 
file-writer-truncate-extend.html 
file-writer-write-overlapped.html 
filesystem-iframe-from-remote.html 
filesystem-url-in-iframe.html 
filesystem-urls-match-self.html 
not-enough-arguments.html 
op-get-metadata.html 
request-file-content.html 
request-metadata.html 
send-file-blob-fail.html 
send-file-blob.html 
shared-worker-constructor.html 

as of:
https://build.chromium.org/p/chromium.webkit/builders/WebKit%20Linux%20Leak/b...

This seems like a likely candidate.


Original issue's description:
> FileWriter should not use deprecated {,un}setPendingActivity
> 
> BUG=354845
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=177936

TBR=nhiroki@chromium.org,tzik@chromium.org,eseidel@chromium.org
NOTRY=true
BUG=354845

Review URL: https://codereview.chromium.org/383993008

git-svn-id: svn://svn.chromium.org/blink/trunk@177988 bbb929c8-8fbe-4397-9dbb-9b2b20218538
IndexedDB: Ensure put() operates on a clone to avoid side effects

The IDBObjectStore.put() and IDBCursor.update() operations do a
number of operations on the value:

1) If inline keys are used, compute the primary key
2) If indexes are used, compute index keys
3) If inline keys and a key generator is used, verify the property
4) If inline keys are used, verify it is not changed (update only)

To avoid these being observable by property getters, these should
all operate on a clone of the original value. This is explicitly
called out in the spec for 1 & 2, and it's probably a spec bug
that the same is not done for 3 & 4.

Since the value is already serialized at the point of these tests,
simply deserialize it as necessary and use the clone. This will
have a performance impact.

BUG=293662

Review URL: https://codereview.chromium.org/23872032

git-svn-id: svn://svn.chromium.org/blink/trunk@177989 bbb929c8-8fbe-4397-9dbb-9b2b20218538