Android ARM: enable PIE.

BUG=

Review URL: https://codereview.chromium.org/757103003

Cr-Commit-Position: refs/heads/master@{#25584}
Do not call Heap::IterateAndMarkPointersToFromSpace() for unboxed double fields.

BUG=chromium:437143
LOG=N

Review URL: https://codereview.chromium.org/768113002

Cr-Commit-Position: refs/heads/master@{#25585}
Improved Makefile.android's readability a bit.

Review URL: https://codereview.chromium.org/770783003

Cr-Commit-Position: refs/heads/master@{#25586}