Non-US OS region generates invalid trace JSON.

base/debug/trace_event_impl.cc

Index: base/debug/trace_event_impl.cc
diff --git a/base/debug/trace_event_impl.cc b/base/debug/trace_event_impl.cc
index 9ee9fc802be105ea979576ec239c6275c467a7fc..6fff9041515d53e7f172dd22f2e2e8b0d9541445 100644
--- a/base/debug/trace_event_impl.cc
+++ b/base/debug/trace_event_impl.cc
@@ -17,6 +17,7 @@
 #include "base/message_loop/message_loop.h"
 #include "base/process/process_metrics.h"
 #include "base/stl_util.h"
+#include "base/strings/string_number_conversions.h"
 #include "base/strings/string_split.h"
 #include "base/strings/string_tokenizer.h"
 #include "base/strings/string_util.h"
@@ -509,9 +510,30 @@ void TraceEvent::AppendValueAsJSON(unsigned char type,
     case TRACE_VALUE_TYPE_INT:
       StringAppendF(out, "%" PRId64, static_cast<int64>(value.as_int));
       break;
-    case TRACE_VALUE_TYPE_DOUBLE:
-      StringAppendF(out, "%f", value.as_double);
+    case TRACE_VALUE_TYPE_DOUBLE: {
+      // FIXME: base/json/json_writer.cc is using the same code,
+      //        should be made into a common method.
+      std::string real = DoubleToString(value.as_double);
+      // Ensure that the number has a .0 if there's no decimal or 'e'.  This
+      // makes sure that when we read the JSON back, it's interpreted as a
+      // real rather than an int.
+      if (real.find('.') == std::string::npos &&
+          real.find('e') == std::string::npos &&
+          real.find('E') == std::string::npos) {
+        real.append(".0");
+      }
+      // The JSON spec requires that non-integer values in the range (-1,1)
+      // have a zero before the decimal point - ".52" is not valid, "0.52" is.
+      if (real[0] == '.') {
+        real.insert(0, "0");
+      } else if (real.length() > 1 && real[0] == '-' && real[1] == '.') {
+        // "-.1" bad "-0.1" good
+        real.insert(1, "0");
+      }
+
+      StringAppendF(out, "%s", real.c_str());
       break;
+    }
     case TRACE_VALUE_TYPE_POINTER:
       // JSON only supports double and int numbers.
       // So as not to lose bits from a 64-bit pointer, output as a hex string.