Reduce how often we call FindDexCache

Before host boot.oat -j4 optimizing compile:
real  1m17.792s
user  3m26.140s
sys 0m8.340s

After:
real  1m12.324s
user  3m22.718s
sys 0m8.320s

Change-Id: If18e9e79e06cdf1676692e5efacb682bf93889c3
diff --git a/compiler/compiler.h b/compiler/compiler.h
index 01ca46e..9b4dbe0 100644
--- a/compiler/compiler.h
+++ b/compiler/compiler.h
@@ -51,7 +51,8 @@
                                   uint16_t class_def_idx,
                                   uint32_t method_idx,
                                   jobject class_loader,
-                                  const DexFile& dex_file) const = 0;
+                                  const DexFile& dex_file,
+                                  Handle<mirror::DexCache> dex_cache) const = 0;
 
   virtual CompiledMethod* JniCompile(uint32_t access_flags,
                                      uint32_t method_idx,