Remove WTF::WeakPtr entirely and replace it with base::WeakPtr.

This CL deletes platform/wtf/WeakPtr.h and replaces and code
that was still using it in WebKit/ with base::WeakPtr(Factory).

In some cases the file was included but was not needed, so
we just delete the header.

Bug: 789697
Cq-Include-Trybots: master.tryserver.chromium.android:android_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel
Change-Id: I60409333fb2cc49be475521b51b65c76824811d9
Reviewed-on: https://chromium-review.googlesource.com/798810
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Stuart Langley <slangley@chromium.org>
Cr-Commit-Position: refs/heads/master@{#521213}
49 files changed