GN: Introduce templates.

Defines the rtc_executable, rtc_source_set, rtc_test and
rtc_static_library templates.

These templates provide no functionality yet, but will enable common
configuration to be introduced, avoiding repetition in every target

Changes summary:
- Prepend rtc_ to test, source_set, executable and static_library targets
- Change "configs -= [" to "suppressed_configs += ["
- Include webrtc/build/webrtc.gni where it wasn't included yet
- Delete import("//testing/test.gni"), since rtc_test makes it unnecessary.

BUG=webrtc:6187
TBR=henrik.lundin@webrtc.org,tommi@webrtc.org
NOTRY=True

Review-Url: https://codereview.webrtc.org/2301053002
Cr-Commit-Position: refs/heads/master@{#14043}
diff --git a/webrtc/common_video/BUILD.gn b/webrtc/common_video/BUILD.gn
index ed5a738..cb1f024 100644
--- a/webrtc/common_video/BUILD.gn
+++ b/webrtc/common_video/BUILD.gn
@@ -7,7 +7,6 @@
 # be found in the AUTHORS file in the root of the source tree.
 
 import("../build/webrtc.gni")
-import("//testing/test.gni")
 
 config("common_video_config") {
   include_dirs = [
@@ -16,7 +15,7 @@
   ]
 }
 
-source_set("common_video") {
+rtc_source_set("common_video") {
   sources = [
     "bitrate_adjuster.cc",
     "h264/h264_common.cc",
@@ -53,7 +52,7 @@
   if (is_clang) {
     # Suppress warnings from Chrome's Clang plugins.
     # See http://code.google.com/p/webrtc/issues/detail?id=163 for details.
-    configs -= [ "//build/config/clang:find_bad_constructs" ]
+    suppressed_configs += [ "//build/config/clang:find_bad_constructs" ]
   }
 
   deps = [
@@ -96,7 +95,7 @@
     }
   }
 
-  test("common_video_unittests") {
+  rtc_test("common_video_unittests") {
     testonly = true
 
     sources = [
@@ -118,7 +117,7 @@
     if (is_clang) {
       # Suppress warnings from the Chromium Clang plugin.
       # See http://code.google.com/p/webrtc/issues/detail?id=163 for details.
-      configs -= [ "//build/config/clang:find_bad_constructs" ]
+      suppressed_configs += [ "//build/config/clang:find_bad_constructs" ]
     }
 
     deps = [