Refactor Subzero initialization and add a browser callback handler.

Makefile

 
 ifndef SUBZERO_LEVEL
 # Top-level, not included from a subdir
 SUBZERO_LEVEL := .
 DIRS := src
 PARALLEL_DIRS :=
 endif
 
 # Set LLVM source root level.
 LEVEL := $(SUBZERO_LEVEL)/../..
 
 # Include LLVM common makefile.
 include $(LEVEL)/Makefile.common
 
 # -O3 seems to trigger the following PNaCl ABI transform bug
 # on method pointers, so override that with -O2:
 # https://code.google.com/p/nativeclient/issues/detail?id=3857
 CXX.Flags += -O2
 # Newlib paired with libc++ requires gnu.
 CXX.Flags += -std=gnu++11
 
 ifeq ($(PNACL_BROWSER_TRANSLATOR),1)
   CPP.Defines += -DALLOW_DUMP=0 -DALLOW_LLVM_CL=0 -DALLOW_LLVM_IR=0 \
     -DALLOW_LLVM_IR_AS_INPUT=0 -DALLOW_DISABLE_IR_GEN=0 \
-    -DALLOW_MINIMAL_BUILD=1
+    -DALLOW_MINIMAL_BUILD=1 -DPNACL_BROWSER_TRANSLATOR=1
 else
   CPP.Defines += -DALLOW_DUMP=1 -DALLOW_LLVM_CL=1 -DALLOW_LLVM_IR=1 \
     -DALLOW_LLVM_IR_AS_INPUT=1 -DALLOW_DISABLE_IR_GEN=1 \
-    -DALLOW_MINIMAL_BUILD=0
+    -DALLOW_MINIMAL_BUILD=0 -DPNACL_BROWSER_TRANSLATOR=0
 endif