Forward declaration for Isolate / Platform in libplatform.h.

Reduces dependencies on #include files, making it easier for other
build systems to include this library.

BUG=

Review URL: https://codereview.chromium.org/740493002

Cr-Commit-Position: refs/heads/master@{#25408}

include/libplatform/libplatform.h

@@ -5,9 +5,11 @@
 #ifndef V8_LIBPLATFORM_LIBPLATFORM_H_
 #define V8_LIBPLATFORM_LIBPLATFORM_H_
 
-#include "include/v8-platform.h"
-
 namespace v8 {
+
+class Isolate;
+class Platform;
+
 namespace platform {
 
 /**

samples/lineprocessor.cc

@@ -29,6 +29,7 @@
 
 #include <include/libplatform/libplatform.h>
 #include <include/v8-debug.h>
+#include <include/v8-platform.h>
 
 #include <fcntl.h>
 #include <stdio.h>

samples/shell.cc

@@ -28,6 +28,7 @@
 #include <include/v8.h>
 
 #include <include/libplatform/libplatform.h>
+#include <include/v8-platform.h>
 
 #include <assert.h>
 #include <fcntl.h>

test/unittests/run-all-unittests.cc

@@ -4,6 +4,7 @@
 
 #include "include/libplatform/libplatform.h"
 #include "include/v8.h"
+#include "include/v8-platform.h"
 #include "src/base/compiler-specific.h"
 #include "testing/gmock/include/gmock/gmock.h"