[Telemetry] Specify all binaries that depends on chrome build
through chrome_root

Since we are about to move telemetry to catapult, paths to
binaries that telemetry need for running that depend on
chromium tree will depend on --chrome-root argument.

To review this patch:
Changes in *_browser_finder.py files are for replacing util.GetChromiumSrcDir() with finder_options.chrome_root.

Changes in benchmark_runner.py & unittest_runner.py is for
piping the default_chrome_root defined by telemetry's
project_config to the command line args.

kbr@: change in browser_finder.py enables using fake
browser options for testing purpose more easily. You should
be able to remove the mock in https://code.google.com/p/chromium/codesearch#chromium/src/content/test/gpu/gpu_tests/gpu_test_base_unittest.py&l=147.
BUG=540501

Review URL: https://codereview.chromium.org/1405113005

Cr-Commit-Position: refs/heads/master@{#355775}
diff --git a/testing/scripts/telemetry_unittests.py b/testing/scripts/telemetry_unittests.py
index 5e41d40..09e3cb62 100755
--- a/testing/scripts/telemetry_unittests.py
+++ b/testing/scripts/telemetry_unittests.py
@@ -21,7 +21,7 @@
     test_args += ['--browser', 'android-chromium', '--device', 'android']
   else:
     test_args += ['--browser', args.build_config_fs.lower()]
-
+  test_args += ['--chrome-root', common.SRC_DIR]
   with common.temporary_file() as tempfile_path:
     test_args += ['--write-full-results-to', tempfile_path]
     rc = common.run_runtest(args, [