Add new prebuilts.

new internal plugin matching I07085
proguard artifacts
some gradle artifacts
slf4j for the gradle-model tests.

Change-Id: Id4c7489b3dab29cfef39cad36a1c41ea293dff10
Merge "Add new prebuilts."
Update Gradle tooling API to 1.6 RC1

Change-Id: I855281a125aa3cc26efe1a1169279ea6ba8390a0
Merge "Update Gradle tooling API to 1.6 RC1"
Add prebuilt for Gradle Tooling API 1.6

Change-Id: I137bd1da6fa683618ca9d27f5803eef45b7a6028
Merge "Add prebuilt for Gradle Tooling API 1.6"
Merge remote-tracking branch 'android/tools_r22'