Teach mojo_shell how to load http URLs

After this CL, we can load content over HTTP. In order to make
that work, I needed to introduce a number of basic concepts
into the shell, including an IO thread and a directory to
store data (such as the HTTP cache).

I've tried to keep the net dependencies separated from the
bulk of the mojo_shell code because I expect we'll want to
move the net dependencies to an app that runs on top of the
Mojo platform rather than linked into the mojo_shell itself.
To that end, the mojo::loader::Loader class doesn't leak any
net headers to its clients.

The version of the loader in this CL is extremely basic. We'll
undoubtedly make it fancier as time goes on. The next step
after this CL is to store the result in a file and then load
that file as a shared object.

R=aa@chromium.org

Review URL: https://codereview.chromium.org/27943002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@229496 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 229496
NaCl: Update revision in DEPS, r12241 -> r12277

This pulls in the following Native Client changes:

r12242: (jvoung) Update LLVM rev to pull in cherrypick of 187787.
r12243: (jvoung) Update PNaCl in TOOL_REVISIONS from 12187 to 12242.
r12244: (jvoung) Bump newlib revision for PNaCl too.
r12245: (khim) Handle a case when gcl is not available
r12246: (jvoung) Update expectations for TestCondvarSignalNoOp, etc. and README for tips.
r12247: (sehr) Make trusted tests work with memcheck....
r12249: (jvoung) Update PNaCl in TOOL_REVISIONS from 12242 to 12244.
r12250: (stichnot) Don't fail early if an exclude file has a problem.
r12251: (jvoung) Turn on some PNaCl mixed / native-object tests now that TC roll finished.
r12252: (mseaborn) Unsandboxed IRT: Add missing "const" to top-level IRT interface structs
r12253: (mseaborn) Unsandboxed IRT: Implement thread+futex interfaces, and some timer interfaces
r12254: (thakis) Store result of | operator in a variable instead of just the filename.
r12255: (khim) Use as/cc/ld flags in all situations
r12256: (petarj) [MIPS] Call AddBiasForPNaCl for float_rounding_mode_test
r12257: (dschuff) Use native objects instead of bitcode objects when building the IRT in debug mode.
r12258: (mcgrathr) Call dummy AssertSameType functions to avoid unused warnings
r12259: (mcgrathr) Remove miscellaneous unused variables and functions
r12260: (stichnot) Update the known failures file, and the llvm-test-suite DEPS.
r12261: (mcgrathr) Conditionalize conditionally-used variable kNaClTempPrefixVar
r12262: (mcgrathr) Update chrome_rev in DEPS
r12264: (mcgrathr) Revert "Update chrome_rev in DEPS"
r12266: (sbc) Roll glibc revision in REVISIONS.
r12267: (jfb) Support iconv to/from UTF-{8,16,32} for newlib (NaCl and PNaCl).
r12268: (jfb) Allow our infrastructure to run libc++ tests.
r12269: (khim) Remove untracked files from git repos
r12270: (dschuff) When building Debug IRT, use -O2 instead of -O0 for the frontend
r12271: (mseaborn) Unsandboxed IRT: Pass argv and environment arrays through to user code
r12272: (stichnot) Update llvm-test-suite DEPS and known-failure lists.
r12273: (dschuff) Use parallel builds in build_nexe.py even without goma
r12274: (jvoung) Avoid passing the made-up --pnacl-* flags to clang.
r12275: (jvoung) Adjust runtime_vortex and ammp for x86-32 and x86-64.
r12276: (jfb) Test that iconv support to/from UTF-{8,16,32} for newlib (NaCl and PNaCl) works.
r12277: (thakis) Improve | logic after r12254.

BUG=none
TEST=nacl_integration

Review URL: https://codereview.chromium.org/29233003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@229497 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 229497