FileAPI: Compare expected modification time with delta on file read

FileAPI: Compare expected modification time with delta on file read

The File API reader validates that the "expected" modification time -
e.g. taken when a user selects a file via <input type=file> matches
the "actual" modification time when trying to read. Certain file
timestamps (on Windows/NTFS at least) are high enough precision
(tenths of microseconds) that an int64->double->int64 round trip
through Blink loses bits. Files with these timestamps can't be read!

Sample timestamp: 2011-01-01T01:23:45.999999Z (that's a lot of 9s)

Make the comparison with an epsilon of 10us.

BUG=525088
R=michaeln@chromium.org

Committed: https://crrev.com/1d45da203ac9fc8ea3f119edf9030d8e948722a3
Cr-Commit-Position: refs/heads/master@{#346802}

[michaeln, 2015-09-01 21:36:22]

lgtm (nice find!)

[jsbell, 2015-09-01 22:27:26]

The CQ bit was checked by jsbell@chromium.org

[commit-bot: I haz the power, 2015-09-01 22:27:47]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1308773006/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1308773006/1

[commit-bot: I haz the power, 2015-09-01 23:42:56]

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

[commit-bot: I haz the power, 2015-09-01 23:42:57]

Try jobs failed on following builders:
  mac_chromium_rel_ng on tryserver.chromium.mac (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.mac/builders/mac_chromium_rel_...)

[jsbell, 2015-09-02 00:09:32]

The CQ bit was checked by jsbell@chromium.org

[jsbell, 2015-09-02 00:09:33]

The patchset sent to the CQ was uploaded after l-g-t-m from
michaeln@chromium.org
Link to the patchset: https://codereview.chromium.org/1308773006/#ps20001
(title: "Remove 20us test since OSX has 1s resolution. ASSERT->EXPECT")

[commit-bot: I haz the power, 2015-09-02 00:09:45]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1308773006/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1308773006/20001

[jsbell, 2015-09-02 00:10:40]

Fun - per https://en.wikipedia.org/wiki/HFS_Plus the OSX filesystem has only 1s
resolution, so trying to touch a file with e.g. a 20us delta won't work.

So... removed that test case, added a note. Also changed ASSERT_EQ to EXPECT_EQ
in that test.

[commit-bot: I haz the power, 2015-09-02 00:55:09]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-09-02 00:55:47]

Patchset 2 (id:??) landed as
https://crrev.com/1d45da203ac9fc8ea3f119edf9030d8e948722a3
Cr-Commit-Position: refs/heads/master@{#346802}