Add specialized .isolated differ that prints unified diff.

Add specialized .isolated differ that prints unified diff.

It prints out unified diff of a human readable version of the .isolated. It
really helps to know what is different in the isolated tree.

R=sebmarchand@chromium.org
BUG=314403
Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=292796

[M-A Ruel, 2014-11-01 23:55:52]

Here's how it looks like here:

d8                    : equal
genmacro              : equal
genmodule             : equal
genperf               : equal
genstring             : equal
genversion            : equal
libffmpegsumo.so      : equal
libosmesa.so          : equal
libvpx_obj_int_extract: equal
mksnapshot            : equal
nacl_irt_x86_64.nexe  : DIFFERENT: 20 out of 3343720 bytes are different (0.00%)
net_unittests         : equal
net_unittests.isolated: equal
protoc                : equal
re2c                  : equal
tls_edit              : equal
unit_tests            : DIFFERENT: 35 out of 191593960 bytes are different
(0.00%)
unit_tests.isolated   : DIFFERENT: 37 out of 1115039 bytes are different (0.00%)
@@ -39346,7 +39346,7 @@

       "s": 11630
     },
     "out/Release/unit_tests": {
-      "h": "f6022f3ab2df3010efbd21489d5c69ed216581a9",
+      "h": "a0642f76a9f52df3f586b6174bf962bad2276d50",
       "m": 360,
       "s": 191593960
     },
xdisplaycheck         : equal
yasm                  : equal
17 files are equal, 3 are different.

[Sébastien Marchand, 2014-11-02 18:35:30]

The CQ bit was checked by sebmarchand@chromium.org

[Sébastien Marchand, 2014-11-02 18:35:31]

lgtm

[commit-bot: I haz the power, 2014-11-02 18:36:25]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/695123002/1

[commit-bot: I haz the power, 2014-11-02 18:37:07]

Committed patchset #1 (id:1) as 292796