Log the Environment ID and the Thread name

To make it easier to debug, add the Environment ID and the Thread name
to the log messages. For instance log messages from the TileParser will look like:

[WARNING] {0}{TileWorker_15/18653/9486}[ParseTile]: some relevant warning message
   |       |             |                  |
   |       |             |                  +-> Component
   |       |             +--------------------> Thread name
   |       +----------------------------------> Environment ID
   +------------------------------------------> Severity level

Log messages that are not inside an Environment::Scope will work
normally and will look like:

[WARNING] [JNI]: some relevant warning message

Fixes #882.

1 files changed, 25 insertions, 1 deletions

diff --git a/src/mbgl/platform/log.cpp b/src/mbgl/platform/log.cpp
index e9712f727c..d6cbc4fd11 100644
--- a/src/mbgl/platform/log.cpp
+++ b/src/mbgl/platform/log.cpp
@@ -1,6 +1,9 @@
 #include <mbgl/platform/log.hpp>
 
+#include <mbgl/map/environment.hpp>
+
 #include <cstdarg>
+#include <sstream>
 
 namespace mbgl {
 
@@ -37,7 +40,28 @@ void Log::record(EventSeverity severity, Event event, int64_t code, const std::s
         return;
     }
 
-    platformRecord(severity, event, code, msg);
+    std::stringstream logStream;
+
+    if (Environment::inScope()) {
+        logStream << "{" << Environment::Get().getID() << "}";
+    }
+
+    const std::string threadName = Environment::threadName();
+    if (!threadName.empty()) {
+        logStream << "{" << threadName << "}";
+    }
+
+    logStream << "[" << event << "]";
+
+    if (code >= 0) {
+        logStream << "(" << code << ")";
+    }
+
+    if (!msg.empty()) {
+        logStream << ": " << msg;
+    }
+
+    platformRecord(severity, logStream.str());
 }
 
 }