Make the blockfile cache an optional build product for chrome target.

net/disk_cache/cache_creator.cc

Index: net/disk_cache/cache_creator.cc
diff --git a/net/disk_cache/cache_creator.cc b/net/disk_cache/cache_creator.cc
index 102e10218abe3f8941b7dac5c79340199fa1be42..23ff396f302169331ff7c13dd4b65c0cc3d8fe7e 100644
--- a/net/disk_cache/cache_creator.cc
+++ b/net/disk_cache/cache_creator.cc
@@ -7,12 +7,15 @@
 #include "base/strings/stringprintf.h"
 #include "net/base/cache_type.h"
 #include "net/base/net_errors.h"
-#include "net/disk_cache/blockfile/backend_impl.h"
 #include "net/disk_cache/cache_util.h"
 #include "net/disk_cache/disk_cache.h"
 #include "net/disk_cache/memory/mem_backend_impl.h"
 #include "net/disk_cache/simple/simple_backend_impl.h"
 
+#ifdef USE_BLOCKFILE_CACHE_BACKEND

[rvargas (doing something else), 2014/01/03 19:56:13]

Can we use OS_ANDROID here?

Having too many knobs and levers is not a good long term strategy and it leads
to not knowing what is being compiled/supported.

I gather that your intention is to remove unit tests for Android, and that's why
I think it is better to avoid an extra configuration axis. However, if your long
term plan is to keep the code unit tested then an extra knob may be needed.

[gavinp, 2014/02/05 20:54:13]

If we use OS_ANDROID here, the expression will be repeated twice in this CL, and
a third time in net.gyp (in a downstream CL). That's a lot of repetitions,
especially since this flag is very useful to set during development.

There's an argument that we don't need to conditionalise the #include here,
since the linker will catch an error if we reference a symbol. That scares me
though, as I enumerate the number of distinct ways in which a header file can
change compilation besides introducing symbols.

[rvargas (doing something else), 2014/02/06 05:09:28]

The number of references seem the same regardless of the name of the symbol.
However, even though now I don't like the way that net _seems_ to have a lot of
configuration options that are not tested (and hence not really well supported),
the fact remains that all knobs on the library are handled the same way: through
a subject-specific gyp variable. In other words, using an OS directly here would
go against the flow.
I lean towards leaving the include in place (we shouldn't be adding code weight
in headers in the first place), but I really don't care that much one way or the
other.

+#include "net/disk_cache/blockfile/backend_impl.h"
+#endif
+
 #ifdef USE_TRACING_CACHE_BACKEND
 #include "net/disk_cache/tracing_cache_backend.h"
 #endif
@@ -91,6 +94,8 @@ int CacheCreator::Run() {
     return simple_cache->Init(
         base::Bind(&CacheCreator::OnIOComplete, base::Unretained(this)));
   }
+
+#if defined(USE_BLOCKFILE_CACHE_BACKEND)
   disk_cache::BackendImpl* new_cache =
       new disk_cache::BackendImpl(path_, thread_.get(), net_log_);
   created_cache_.reset(new_cache);
@@ -101,6 +106,9 @@ int CacheCreator::Run() {
       base::Bind(&CacheCreator::OnIOComplete, base::Unretained(this)));
   DCHECK_EQ(net::ERR_IO_PENDING, rv);
   return rv;
+#else
+  return net::ERR_FAILED;
+#endif
 }
 
 void CacheCreator::DoCallback(int result) {