Revert Junov's last two CLs (per his request) in an attempt to fix Debug ASSERT_NOT_REACHED

We've had a marauding ASSERT_NOT_REACHED related to canvas this afternoon.
Junov believes its caused by his last two CL's and has asked me to rever them.

Revert "Fixing Canvas2DLayerBridge to handle lost graphics contexts"

This reverts commit c9a24ca0534f2aaf6e0182fb4ba3c90e6cbb1315.

Revert "Removed duplicated line of code in Canvas2DLayerBridge due to merge conflict resolution error"

This reverts commit 0f77c35b3e8b2fd14b46782b5f79908fbc16f15f.

BUG=240881, 226928, 237799
TBR=junov

Review URL: https://codereview.chromium.org/18414009

git-svn-id: svn://svn.chromium.org/blink/trunk@154149 bbb929c8-8fbe-4397-9dbb-9b2b20218538