Get gn generation working on mac

This fixes a few minor issues so initial gn generation passes and the
'base' target can be built. Specifically:
- fixes so ldflags in the compiler config
- update to_build_path() calls to rebase_path() calls
- comment out some deps on nss targets that don't exist yet

R=brettw

Review URL: https://codereview.chromium.org/25583005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226591 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 226591
Change SkMScalar from double to float

BUG=269817

Review URL: https://codereview.chromium.org/23477072

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226592 0039d316-1c4b-4281-b951-d872f2087c98
r226421 added 10.9 as a variant, so it should be valid.

TEST=none
BUG=

Review URL: https://codereview.chromium.org/25657007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226593 0039d316-1c4b-4281-b951-d872f2087c98
Fix SyncFileSystemServiceTest.SimpleLocalSyncFlow

- Fixed OnWriteEnabled/OnSyncEnabled expectations for LocalSync,
  as we now enable writing before a local sync finishes.
- Added more verbose comment in LocalFileSyncContext.

BUG=237710
TEST=SyncFileSystemServiceTest.SimpleLocalSyncFlow

Review URL: https://codereview.chromium.org/25679002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226594 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 226594