[heap] Hide MemoryReducer inside the heap component.

[heap] Hide MemoryReducer inside the heap component.

This prevents leakage of the memory-reducer.h declarations inside of the
heap and prevents it from being exposed to the world. Protects private
state from being inadvertently mocked with.

R=mlippautz@chromium.org

Committed: https://crrev.com/de57a6c0609aa9ab43cea474d252178ba044d448
Cr-Commit-Position: refs/heads/master@{#30277}

[Michael Lippautz, 2015-08-20 16:45:46]

lgtm

[Michael Starzinger, 2015-08-20 16:47:16]

The CQ bit was checked by mstarzinger@chromium.org

[commit-bot: I haz the power, 2015-08-20 16:47:32]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1288913003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1288913003/1

[commit-bot: I haz the power, 2015-08-20 16:48:45]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-08-20 16:48:58]

Patchset 1 (id:??) landed as
https://crrev.com/de57a6c0609aa9ab43cea474d252178ba044d448
Cr-Commit-Position: refs/heads/master@{#30277}