Small fix for the timer event plotter.

Sometimes v8.log entries are cut off, and leave an unpaired quote.
Since the log is piped into d8 to run the tick processor, that quote
is interpreted to escape a line break.

This fix makes sure that we break lines even with unpaired quotes.

R=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/1802303002

Cr-Commit-Position: refs/heads/master@{#34786}

tools/profviz/composer.js

@@ -331,7 +331,7 @@ function PlotScriptComposer(kResX, kResY, error_output) {
 
     var line;
     while (line = input()) {
-      logreader.processLogLine(line);
+      for (var s of line.split("\n")) logreader.processLogLine(s);
     }
 
     // Collect execution pauses.