Share command flags between dm and unit tests.
Also, allow dm's core to be included by itself and iOSShell.
Command line flags that are the same (or nearly the same) in DM
and in skia_tests have been moved to common_flags. Authors,
please check to see that the shared common flag is correct for
the tool.
For iOS, the 'tool_main' entry point has a wrapper to allow multiple
tools to be statically linked in the iOSShell.
Since SkCommandLineFlags::Parse can only be called once, these calls
are disabled in the IOS build.
Since the iOS app directory is dynamically assigned a name, use '@' to
select it. (This is the same convention chosen by the Mobile Harness
iOS file system utilities.)
Move the heart of dm.gyp into dm.gypi so that it can be included by
itself and iOSShell.gyp.
Add tools/flags/SkCommonFlags.* to define and declare common
command line flags.
Add support for dm to iOSShell.
BUG=skia:
R=scroggo@google.com, mtklein@google.com, jvanverth@google.com, bsalomon@google.com
Author: caryclark@google.com
Review URL: https://codereview.chromium.org/389653004
