[telemetry] Create BrowserTestCase to reuse the browser for browser_unittest.

[telemetry] Create BrowserTestCase to reuse the browser for browser_unittest.

This brings browser_unittest's run time from 21s to 7s on a Z620 Linux, one of our fastest
configurations. (We still need 3 browser launches to test browser options and profile loading.)

Add BrowserTestCase as the new parent class of TabTestCase. The separation is very clean :)
Also add helper method UrlOfUnittestFile - many tests are using http_server.UrlOf incorrectly,
and this helper ensures the HTTP server is running and we're pointing to the right file.
Also move page_test_test_case from testing/ to unittest/ and remove testing/.


BUG=388256
TEST=tools/telemetry/run_tests

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=289247

[tonyg, 2014-08-13 02:00:44]

The CQ bit was checked by tonyg@chromium.org

[tonyg, 2014-08-13 02:00:44]

lgtm

[commit-bot: I haz the power, 2014-08-13 02:02:50]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/dtu@chromium.org/469593002/40001

[nduca, 2014-08-13 03:38:53]

this looks very promising, and is the right route forward. lgtm very much.

[tonyg, 2014-08-13 04:03:44]

CQ failure is legit:

ImportError: No module named testing

[commit-bot: I haz the power, 2014-08-13 05:00:02]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  linux_chromium_rel_swarming on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...)
  mac_chromium_rel_swarming on tryserver.chromium.mac
(http://build.chromium.org/p/tryserver.chromium.mac/builders/mac_chromium_rel_...)
  win_chromium_rel_swarming on tryserver.chromium.win
(http://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_rel_...)
  win_chromium_x64_rel on tryserver.chromium.win
(http://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_x64_...)

[dtu, 2014-08-13 05:00:39]

The CQ bit was checked by dtu@chromium.org

[commit-bot: I haz the power, 2014-08-13 05:02:57]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/dtu@chromium.org/469593002/60001

[commit-bot: I haz the power, 2014-08-13 10:06:52]

Change committed as 289247