Rename "tree of trees" to "composed tree".

This is another renaming after r374095.
This CL is the result of the (almost) mechanical renaming, using:

> git ls-files | egrep '(html|txt|cpp|h|idl|js)$' | xargs sed -i -e 's/tree of trees/composed tree/g' \
> -e 's/Tree of trees/Composed tree/g' -e 's/TreeOfTrees/ComposedTree/g' -e 's/treeOfTrees/composedTree/g'

BUG=531990

Review URL: https://codereview.chromium.org/1684533002

Cr-Commit-Position: refs/heads/master@{#374364}
87 files changed