Revert of [GN] Don't rewrite files with the same contents (patchset #5 id:80001 of https://codereview.chromium.org/1656253003/ )

Reason for revert:
Need to revert this patch according https://sites.google.com/a/chromium.org/dev/developers/tree-sheriffs/sheriffing-bug-queues. This patch added a flaky test FilesystemUtils.WriteFileIfChanged.

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It's a test flake:
1) Try to find the patch that caused the flake. It should be recent (e.g. last day or two) in all likelihood.
2) If successful with finding that patch, revert the patch. This is especially true if the flake is from a new test introduced in that patch.
3) Close the bug.

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The test has failed in the following builds:

http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_rel_ng/builds/176911
http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_rel_ng/builds/176911
http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_rel_ng/builds/176735
http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_rel_ng/builds/176715
http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_rel_ng/builds/176715
http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_rel_ng/builds/176561
http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_rel_ng/builds/176462
http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_rel_ng/builds/176375

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Example failure:

[ RUN      ] FilesystemUtils.WriteFileIfChanged
../../tools/gn/filesystem_utils_unittest.cc:610: Failure
Expected: (last_modified) != (file_info.last_modified), actual: 2016-02-04 18:06:36.920 UTC vs 2016-02-04 18:06:36.920 UTC
[  FAILED  ] FilesystemUtils.WriteFileIfChanged (3 ms)
[315/315] FilesystemUtils.WriteFileIfChanged (3 ms)
Retrying 1 test (retry #2)
[ RUN      ] FilesystemUtils.WriteFileIfChanged
../../tools/gn/filesystem_utils_unittest.cc:610: Failure
Expected: (last_modified) != (file_info.last_modified), actual: 2016-02-04 18:06:36.936 UTC vs 2016-02-04 18:06:36.936 UTC
[  FAILED  ] FilesystemUtils.WriteFileIfChanged (2 ms)
[316/316] FilesystemUtils.WriteFileIfChanged (2 ms)
Retrying 1 test (retry #3)
[ RUN      ] FilesystemUtils.WriteFileIfChanged
../../tools/gn/filesystem_utils_unittest.cc:610: Failure
Expected: (last_modified) != (file_info.last_modified), actual: 2016-02-04 18:06:36.952 UTC vs 2016-02-04 18:06:36.952 UTC
[  FAILED  ] FilesystemUtils.WriteFileIfChanged (2 ms)
[317/317] FilesystemUtils.WriteFileIfChanged (2 ms)
1 test failed:
    FilesystemUtils.WriteFileIfChanged (../../tools/gn/filesystem_utils_unittest.cc:579)

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More details in http://crbug.com/584548.

Original issue's description:
> [GN] Don't rewrite files with the same contents
>
> BUG=
>
> Committed: https://crrev.com/f8ea5cceefcedd4a01935d5ac4d2ba71e23ac13e
> Cr-Commit-Position: refs/heads/master@{#373544}

TBR=brettw@chromium.org,tmoniuszko@opera.com
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG=

Review URL: https://codereview.chromium.org/1672783002

Cr-Commit-Position: refs/heads/master@{#373882}
6 files changed