android: Wait for Chrome to finish writing trace file before downloading

When downloading the latest trace file from Chrome, wait for Chrome to
actually finish writing it to avoid getting back a partially written
trace.

Chrome logs two different messages related to tracing:

1. "Logging performance trace to file [...]"
2. "Profiler finished. Results are in [...]"

The first one is printed when tracing starts and the second one indicates
that the trace file is ready to be downloaded.

We have to look for both of these messages to make sure we get the results
from the latest trace and that the trace file is complete. This is done by
first looking for the last instance of the first message and then checking
for the second message in the remaining part of the log.

Review URL: https://chromiumcodereview.appspot.com/23477016

git-svn-id: http://src.chromium.org/svn/trunk/src/build@220298 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

android/adb_profile_chrome

@@ -43,14 +43,45 @@ send_intent() {
 }
 
 download_latest_trace() {
-  TRACE_FILE=$(adb logcat -d | \
-      grep "Logging performance trace to file: " | \
-      tail -1 | \
-      perl -pi -e "s/.*\/storage\/emulated\/.+\/([^\r]+).*/\/sdcard\/Download\/\\1/g")
-  if [ -z "$TRACE_FILE" ]; then
-    echo "Unable to determine trace file name"
-    exit 1
-  fi
+  (adb logcat -d | grep -q "Logging performance trace to file") || {
+    echo "WARNING: Trace start marker not found. Is the correct version of Chrome running?"
+  }
+
+  local ITERATION=0
+  while true; do
+    # Chrome logs two different messages related to tracing:
+    #
+    # 1. "Logging performance trace to file [...]"
+    # 2. "Profiler finished. Results are in [...]"
+    #
+    # The first one is printed when tracing starts and the second one indicates
+    # that the trace file is ready to be downloaded.
+    #
+    # We have to look for both of these messages to make sure we get the results
+    # from the latest trace and that the trace file is complete. This is done by
+    # first looking for the last instance of the first message and then checking
+    # for the second message in the remaining part of the log.
+    TRACE_FILE=$(adb logcat -d | \
+        tac | \
+        grep --max-count=1 --before-context=100000 "Logging performance trace to file" | \
+        tac | \
+        grep "Profiler finished[.] Results are in " | \
+        perl -pi -e "s{.*/storage/emulated/.+/([^\r]+)[.].*}{/sdcard/Download/\\1}g")
+    if [ -n "$TRACE_FILE" ]; then
+      break
+    fi
+    if [ $ITERATION -eq 0 ]; then
+      echo -n "Waiting for Chrome to finish tracing..."
+    else
+      echo -n "."
+    fi
+    let ITERATION=ITERATION+1
+    if [ $ITERATION -eq 60 ]; then
+      echo "Timed out"
+      exit 1
+    fi
+    sleep 1
+  done
 
   adb pull $TRACE_FILE 2> /dev/null
   LOCAL_TRACE_FILE=$(basename $TRACE_FILE)
@@ -72,7 +103,6 @@ do_timed_capture() {
   echo "done"
 
   echo -n "Downloading trace..."
-  sleep $[${INTERVAL} / 4 + 1]
   download_latest_trace
   echo "done"