Improve documentation about StringFactory.newStringFromChars.

Make it clear that the native method requires its third
argument to be non-null, and therefore that the intrinsics
do not need a null check for it.

Bug: 27378573
Change-Id: Id2f78ceb0f7674f1066bc3f216b738358ca25542
diff --git a/compiler/dex/quick/gen_invoke.cc b/compiler/dex/quick/gen_invoke.cc
index 422d82f..fa7c961 100755
--- a/compiler/dex/quick/gen_invoke.cc
+++ b/compiler/dex/quick/gen_invoke.cc
@@ -1140,6 +1140,12 @@
   RegLocation rl_offset = info->args[0];
   RegLocation rl_count = info->args[1];
   RegLocation rl_data = info->args[2];
+  // No need to emit code checking whether `rl_data` is a null
+  // pointer, as callers of the native method
+  //
+  //   java.lang.StringFactory.newStringFromChars(int offset, int charCount, char[] data)
+  //
+  // all include a null check on `data` before calling that method.
   CallRuntimeHelperRegLocationRegLocationRegLocation(
       kQuickAllocStringFromChars, rl_offset, rl_count, rl_data, true);
   RegLocation rl_return = GetReturn(kRefReg);