Print less output from compare_videos.py in WebRTC quality test.

chrome/browser/media/chrome_webrtc_video_quality_browsertest.cc

Index: chrome/browser/media/chrome_webrtc_video_quality_browsertest.cc
diff --git a/chrome/browser/media/chrome_webrtc_video_quality_browsertest.cc b/chrome/browser/media/chrome_webrtc_video_quality_browsertest.cc
index b5ffbc841ea077b7cae1f44b1cf8957d21584509..227de2e40c2dc179e556790888e6c5936fd2b7a6 100644
--- a/chrome/browser/media/chrome_webrtc_video_quality_browsertest.cc
+++ b/chrome/browser/media/chrome_webrtc_video_quality_browsertest.cc
@@ -283,9 +283,20 @@ class WebrtcVideoQualityBrowserTest : public WebRtcTestBase {
     VLOG(0) << "Running " << compare_command.GetCommandLineString();
     std::string output;
     bool ok = base::GetAppOutput(compare_command, &output);
+
+    size_t first_result_line_pos = output.find("RESULT");
+    if (first_result_line_pos == std::string::npos) {
+      LOG(ERROR) << "Got unexpected output from compare_videos.py:"
+                 << output;
+      return false;
+    }
+
     // Print to stdout to ensure the perf numbers are parsed properly by the
-    // buildbot step.
-    printf("Output was:\n\n%s\n", output.c_str());
+    // buildbot step. Only print the result lines to ensure we write all of
+    // it before we hit some os buffer limit and give other processes the
+    // chance to write to Chrome's stdout.
+    std::string result_lines = output.substr(first_result_line_pos);
+    printf("Output was:\n\n%s\n", result_lines.c_str());
     return ok;
   }