Fix build flakiness resulting from mutating globals in chromium_tests.
Fix build flakiness resulting from mutating globals in chromium_tests.

The chromium_tests recipe module would return references to static
objects, but the recipe tests would then mutate them. This could
lead to flaky test failures.

This patch changes the module api to only return copies of the static
objects, so that the static objects themselves are never mutated.

R=phajdan.jr@chromium.org, luqui@chromium.org, iannucci@chromium.org
BUG=553925

Review URL: https://codereview.chromium.org/1509953004

git-svn-id: 239fca9b83025a0b6f823aeeca02ba5be3d9fd76@297950 0039d316-1c4b-4281-b951-d872f2087c98

eunchong/build,eunchong/build,eunchong/build,eunchong/build