Reland again [Startup Tracing] Add --trace-config-file flag

Reland again [Startup Tracing] Add --trace-config-file flag

Original CL: https://codereview.chromium.org/1315463002/
1st reland: https://codereview.chromium.org/1317333002/

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This CL adds --trace-config-file flag. Please see trace_config_file.h for details.

Design doc:
https://docs.google.com/document/d/1PgdXUOJF3WtEmYWUyGRbC2Fz2ICCZKO9jPvpLPRSHH8/edit?usp=sharing

BUG=317481, 482098
TBR=dsinclair@chromium.org,blundell@chromium.org,sievers@chromium.org,sky@chromium.org,msw@chromium.org

Committed: https://crrev.com/c074d28f557ee0996efb3aa584b8932e1beb837e
Cr-Commit-Position: refs/heads/master@{#346407}

[Zhen Wang, 2015-08-31 16:19:04]

The compile error on Win x64 GN is now fixed. The trybot verion for that is
win_chromium_gn_x64_rel.

For the 1st patch set (unmodified):
The compile error was caused by the unit test. 

For the 2nd patch set (with fix):
The unit test was compiled without any problem. The compile error was caused by
insufficient disk space to complete link.

So relanding this CL with TBR. I will also watch the waterfall just in case.

[Zhen Wang, 2015-08-31 16:19:11]

The CQ bit was checked by zhenw@chromium.org

[commit-bot: I haz the power, 2015-08-31 16:19:32]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1309243004/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1309243004/20001

[commit-bot: I haz the power, 2015-08-31 17:28:28]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-08-31 17:29:04]

Patchset 2 (id:??) landed as
https://crrev.com/c074d28f557ee0996efb3aa584b8932e1beb837e
Cr-Commit-Position: refs/heads/master@{#346407}