[libfuzzer] Update GN flags for reproducing bugs.

testing/libfuzzer/reproducing.md

Index: testing/libfuzzer/reproducing.md
diff --git a/testing/libfuzzer/reproducing.md b/testing/libfuzzer/reproducing.md
index beac2bed7e783e51566f91843b8fc38b2def053f..309ba7b6e5f7da57322699d1db4f3bdefccfdad6 100644
--- a/testing/libfuzzer/reproducing.md
+++ b/testing/libfuzzer/reproducing.md
@@ -43,9 +43,15 @@ additional information/links.
    `libfuzzer_chrome_ubsan`, indicating which one to use.
 
 
+*Note*: ClusterFuzz uses release builds by default, so it may be worth adding
+`is_debug=false` to your GN args if you are having trouble reproducing a
+particular report. For ASan builds both Debug and Release configurations are
+supported. Check a job type of the report for presence of `_debug` suffix.
+
+
 ### Reproducing AFL + ASan bugs
 ```bash
-$ gn gen out/afl '--args=use_afl=true is_asan=true enable_nacl=false proprietary_codecs=true'
+$ gn gen out/afl '--args=use_afl=true is_asan=true enable_nacl=false proprietary_codecs=true ffmpeg_branding="Chrome"'

[inferno, 2016/08/26 14:45:26]

Most devs will be using is_debug=false, so lets make it default for asan too.
and then fix your above comment.

Also, add point about ffmpeg_branding=ChromeOS for linux, ffmpeg_branding=Chrome
for other platforms.

[mmoroz, 2016/08/26 16:35:59]

Done.

 $ ninja -C out/afl $FUZZER_NAME
 $ out/afl/$FUZZER_NAME < /path/to/repro
 ```
@@ -53,7 +59,7 @@ $ out/afl/$FUZZER_NAME < /path/to/repro
 ### Reproducing LibFuzzer + ASan bugs
 
 ```bash
-$ gn gen out/libfuzzer '--args=use_libfuzzer=true is_asan=true enable_nacl=false proprietary_codecs=true'
+$ gn gen out/libfuzzer '--args=use_libfuzzer=true is_asan=true enable_nacl=false proprietary_codecs=true ffmpeg_branding="Chrome"'
 $ ninja -C out/libfuzzer $FUZZER_NAME
 $ out/libfuzzer/$FUZZER_NAME /path/to/repro
 ```
@@ -63,7 +69,7 @@ $ out/libfuzzer/$FUZZER_NAME /path/to/repro
 ```bash
 # The gclient sync is necessary to pull in instrumented libraries.
 $ GYP_DEFINES='msan=1 use_prebuilt_instrumented_libraries=1' gclient sync
-$ gn gen out/libfuzzer '--args=use_libfuzzer=true is_msan=true msan_track_origins=2 use_prebuilt_instrumented_libraries=true enable_nacl=false proprietary_codecs=true'
+$ gn gen out/libfuzzer '--args=is_debug=false use_libfuzzer=true is_msan=true msan_track_origins=2 use_prebuilt_instrumented_libraries=true enable_nacl=false proprietary_codecs=true ffmpeg_branding="Chrome"'
 $ ninja -C out/libfuzzer $FUZZER_NAME
 $ out/libfuzzer/$FUZZER_NAME /path/to/repro
 ```
@@ -71,12 +77,9 @@ $ out/libfuzzer/$FUZZER_NAME /path/to/repro
 ### Reproducing LibFuzzer + UBSan bugs
 
 ```bash
-$ gn gen out/libfuzzer '--args=use_libfuzzer=true is_ubsan_security=true enable_nacl=false proprietary_codecs=true'
+$ gn gen out/libfuzzer '--args=is_debug=false use_libfuzzer=true is_ubsan_security=true enable_nacl=false proprietary_codecs=true ffmpeg_branding="Chrome"'
 $ ninja -C out/libfuzzer $FUZZER_NAME
 $ export UBSAN_OPTIONS=halt_on_error=1:print_stacktrace=1
 $ out/libfuzzer/$FUZZER_NAME /path/to/repro
 ```
 
-*Note*: ClusterFuzz uses release builds by default, so it may be worth adding
-"is_debug=false" to your GN args if you are having trouble reproducing a
-particular report.