GN: Use implicit dependency for binary input deps

tools/gn/variables.cc

Index: tools/gn/variables.cc
diff --git a/tools/gn/variables.cc b/tools/gn/variables.cc
index 3c717d82ed60346525b47141581c1cef0e613b35..76305f588631e94f7f3c90a48696faf4b8dbb4b4 100644
--- a/tools/gn/variables.cc
+++ b/tools/gn/variables.cc
@@ -1048,13 +1048,11 @@ const char kInputs_Help[] =
     "  files in a target are compiled. So if you depend on generated headers,\n"
     "  you do not typically need to list them in the inputs section.\n"
     "\n"
-    "  Inputs for binary targets will be treated as order-only dependencies,\n"
-    "  meaning that they will be forced up to date before compiling or\n"
-    "  any files in the target, but changes in the inputs will not\n"
-    "  necessarily force the target to compile. This is because it is\n"
-    "  expected that the compiler will report the precise list of input\n"
-    "  dependencies required to recompile each file once the initial build\n"
-    "  is done.\n"
+    "  Inputs for binary targets will be treated as implicit dependencies,\n"
+    "  meaning that changes in the inputs will force the target to compile.\n"

[brettw, 2016/06/17 17:54:20]

How about:

...changes in any of the inputs will force all sources in the target to be
recompiled. If an input only applies to a subset of source files, you may want
to split those into a separate target to avoid unnecessary recompiles.

[Petr Hosek, 2016/06/17 18:59:30]

Done.

+    "  This may cause unnecessarily recompiles since every source has an\n"
+    "  implicit dependency on all inputs. Therefore, it is recommended to\n"
+    "  place the sources together with their inputs into separate targets.\n"
     "\n"
     "Example\n"
     "\n"