Reland of land "Turn libbase into a component"

src/base/platform/platform.h

Index: src/base/platform/platform.h
diff --git a/src/base/platform/platform.h b/src/base/platform/platform.h
index d3b6c9c1cf3d758276ccc39c50a20b51fc9f9f98..5d570e7048b6d1fc4b600cfd3f9e38ba397e4a18 100644
--- a/src/base/platform/platform.h
+++ b/src/base/platform/platform.h
@@ -25,6 +25,7 @@
 #include <string>
 #include <vector>
 
+#include "src/base/base-export.h"
 #include "src/base/build_config.h"
 #include "src/base/compiler-specific.h"
 #include "src/base/platform/mutex.h"
@@ -69,7 +70,7 @@
 
 #define V8_FAST_TLS_SUPPORTED 1
 
-extern intptr_t kMacTlsBaseOffset;
+extern V8_BASE_EXPORT intptr_t kMacTlsBaseOffset;
 
 INLINE(intptr_t InternalGetExistingThreadLocal(intptr_t index));
 
@@ -102,7 +103,7 @@
 // functions. Add methods here to cope with differences between the
 // supported platforms.
 
-class OS {
+class V8_BASE_EXPORT OS {
  public:
   // Initialize the OS class.
   // - random_seed: Used for the GetRandomMmapAddress() if non-zero.
@@ -211,7 +212,7 @@
     char text[kStackWalkMaxTextLen];
   };
 
-  class MemoryMappedFile {
+  class V8_BASE_EXPORT MemoryMappedFile {
    public:
     virtual ~MemoryMappedFile() {}
     virtual void* memory() const = 0;
@@ -286,7 +287,7 @@
 // Control of the reserved memory can be assigned to another VirtualMemory
 // object by assignment or copy-contructing. This removes the reserved memory
 // from the original object.
-class VirtualMemory {
+class V8_BASE_EXPORT VirtualMemory {
  public:
   // Empty VirtualMemory object, controlling no reserved memory.
   VirtualMemory();
@@ -418,7 +419,7 @@
 // thread. The Thread object should not be deallocated before the thread has
 // terminated.
 
-class Thread {
+class V8_BASE_EXPORT Thread {
  public:
   // Opaque data type for thread-local storage keys.
   typedef int32_t LocalStorageKey;