[tools] Manually write JSON in profile.js to avoid huge strings

tools/profile.js

 // Copyright 2009 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 951 matching lines @@
     if (resolved) {
       processedStack.push(resolved.entry.codeId, resolved.offset);
     } else {
       processedStack.push(-1, stack[i]);
     }
   }
   this.ticks_.push({ tm : time_ns, vm : vmState, s : processedStack });
 };
 
 JsonProfile.prototype.writeJson = function() {
-  var toplevel = {
-    code : this.codeEntries_,
-    functions : this.functionEntries_,
-    ticks : this.ticks_
-  };
-  write(JSON.stringify(toplevel));
+  // Write out the JSON in a partially manual way to avoid creating too-large
+  // strings in one JSON.stringify call when there are a lot of ticks.
+  write('{\n')
+  write('  "code": ' + JSON.stringify(this.codeEntries_) + ',\n');
+  write('  "functions": ' + JSON.stringify(this.functionEntries_) + ',\n');
+  write('  "ticks": [\n');
+  for (var i = 0; i < this.ticks_.length; i++) {
+    write('    ' + JSON.stringify(this.ticks_[i]));
+    if (i < this.ticks_.length - 1) {
+      write(',\n');
+    } else {
+      write('\n');
+    }
+  }
+  write('  ]\n');
+  write('}\n');
 };