Expose a way to obtain a unique ID for the current process.

public/platform/Platform.h

Index: public/platform/Platform.h
diff --git a/public/platform/Platform.h b/public/platform/Platform.h
index 7b8f0f648177cd1162c765da71fb29574fe85419..5b0eda845bc5f29efeeed690311646f1753fb719 100644
--- a/public/platform/Platform.h
+++ b/public/platform/Platform.h
@@ -294,6 +294,12 @@ public:
     // See comments on ImageDecoder::m_maxDecodedBytes.
     virtual size_t maxDecodedImageBytes() { return noDecodedImageByteLimit; }
 
+    // Process -------------------------------------------------------------
+
+    // Returns a unique identifier for a process. This may not necessarily be
+    // the process's process ID.
+    virtual uint32_t getUniqueIdForProcess() { return 0; }
+
 
     // Message Ports -------------------------------------------------------