When we use replaceChildNode function, the first argument must be the original
child node instead of the deepCopy. Otherwise, replaceChildNode will do nothing
since it will think deepCopy is a different node. In that case,
RewriteExpressionsWithShaderStorageBlockTraverser::visitAggregate will
enter an endless loop since ssbo argument is never really replaced.

Test: dEQP-GLES31.functional.ssbo.*
Bug: angleproject:1951
Change-Id: Ieb17a16ab2b3e0270328fafd7ba0944ca05f842f
Reviewed-on: https://chromium-review.googlesource.com/c/1446686Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jiajia Qin <jiajia.qin@intel.com>