Allow single-argument StrCat

and modify DEPS files accordingly.
This is done in support of the decision to encourage AbslStringify.

Bug: None
Change-Id: I26fee77978d1dd21be6d2ef011c4dfd78a7b43e0
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/367204
Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
Commit-Queue: Harald Alvestrand <hta@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#43338}

DEPS

@@ -2125,6 +2125,7 @@ include_rules = [
   "+absl/strings/ascii.h",
   "+absl/strings/escaping.h",
   "+absl/strings/match.h",
+  "+absl/strings/str_cat.h",  # note - allowed for single argument version only
   "+absl/strings/str_replace.h",
   "+absl/strings/string_view.h",
   "+absl/types/variant.h",

api/DEPS

@@ -261,8 +261,4 @@ specific_include_rules = {
     "+video",
     "+third_party",
   ],
-
-  "jsep_unittest\.cc": [
-    "+absl/strings/str_cat.h",
-  ]
 }

g3doc/abseil-in-webrtc.md

@@ -44,6 +44,7 @@ on a monolithic Abseil build target that will generate a shared library.
 * The macros in `absl/base/attributes.h`, `absl/base/config.h` and
   `absl/base/macros.h`.
 * `absl/numeric/bits.h`
+* Single argument absl::StrCat
 
 * ABSL_FLAG is allowed in tests and tools, but disallowed in in non-test code.
 
@@ -78,3 +79,7 @@ we will consider replacing `rtc::ArrayView` with `std::span`.
 These are optimized for speed, not binary size. Even `StrCat` calls
 with a modest number of arguments can easily add several hundred bytes
 to the binary.
+
+Exception: Single-argument absl::StrCat is allowed in order to make it
+easy to use AbslStringify. See [TOTW #2015](https://abseil.io/tips/215) for
+details on AbslStringify.

media/DEPS

@@ -40,7 +40,4 @@ specific_include_rules = {
   ".*codec\.h": [
     "+absl/strings/str_format.h",
   ],
-  ".*codec_unittest\.cc": [
-    "+absl/strings/str_cat.h",
-  ],
 }

rtc_base/DEPS

@@ -8,10 +8,6 @@ include_rules = [
 specific_include_rules = {
   "checks.h": [
     "+absl/strings/has_absl_stringify.h",
-    "+absl/strings/str_cat.h",
-  ],
-  "string_encode.h": [
-    "+absl/strings/str_cat.h"
   ],
   "protobuf_utils.h": [
     "+third_party/protobuf",
@@ -27,7 +23,6 @@ specific_include_rules = {
   ],
   "logging.h": [
     "+absl/strings/has_absl_stringify.h",
-    "+absl/strings/str_cat.h",
   ],
   "trace_event\.h": [
     "+third_party/perfetto",