Revert 238025 "Let test_isolation_mode default to check on mac."

Failing on "Google Chrome Mac" (http://build.chromium.org/p/chromium.chrome/builders/Google%20Chrome%20Mac/builds/15042)
In the error log, tools/swarming_client/isolate.py says "File /Volumes/data/b/build/slave/google-chrome-rel-mac/build/src/out/Release/Chromium Framework.framework doesn't exist"

> Let test_isolation_mode default to check on mac.
> 
> It was set to noop in https://chromiumcodereview.appspot.com/14055005 due to
> issues with xcode. Now that xcode is no longer used, it can be set to check
> again.
> 
> BUG=none
> 
> Review URL: https://codereview.chromium.org/92303002

TBR=thakis@chromium.org

Review URL: https://codereview.chromium.org/98383002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@238036 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 238036
AppListPositioner::GetShelfEdge: Added a missing check.

This could erroneously cause it to return an edge when it should have
returned UNKNOWN.

Also changed tests so they include a Mac-style menu bar. (This helped
expose this bug, and will be useful for testing Mac-specific changes.)

BUG=324383

Review URL: https://codereview.chromium.org/96053003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@238037 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 238037