Merge all StyleSheetCollections.

Merge all StyleSheetCollections.

We don't need all these subtypes, or to create the base class as to
what amounts to a thin wrapper around a Vector. Instead lets merge all
the types together. Future patches will remove the special cases inside
the collection for Document vs ShadowRoot.

R=eseidel@chromium.org

Committed: https://chromium.googlesource.com/external/mojo/+/b32f998e845b1761cd05fc6dc62f9ec977e75141

[eseidel, 2014-12-16 03:46:22]

eseidel@chromium.org changed reviewers:
+ eseidel@chromium.org

[eseidel, 2014-12-16 03:46:22]

The CQ bit was checked by eseidel@chromium.org

[eseidel, 2014-12-16 03:46:22]

lgtm

[commit-bot: I haz the power, 2014-12-16 03:49:44]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-12-16 03:49:45]

Commit queue rejected this change because it did not recognize the base URL.
Please commit your change manually.

[esprehn, 2014-12-16 20:41:20]

Committed patchset #1 (id:1) manually as
b32f998e845b1761cd05fc6dc62f9ec977e75141 (presubmit successful).