Remove grab-bag includes of v8.h from everywhere.

src/snapshot/snapshot.h

 // Copyright 2006-2008 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+#ifndef V8_SNAPSHOT_SNAPSHOT_H_
+#define V8_SNAPSHOT_SNAPSHOT_H_
+
 #include "src/isolate.h"
 #include "src/snapshot/serialize.h"
 
-#ifndef V8_SNAPSHOT_SNAPSHOT_H_
-#define V8_SNAPSHOT_SNAPSHOT_H_
-
 namespace v8 {
 namespace internal {
 
+// Forward declarations.
+class Isolate;
+class PartialSerializer;
+class StartupSerializer;
+
 class Snapshot : public AllStatic {
  public:
   class Metadata {
    public:
     explicit Metadata(uint32_t data = 0) : data_(data) {}
     bool embeds_script() { return EmbedsScriptBits::decode(data_); }
     void set_embeds_script(bool v) {
       data_ = EmbedsScriptBits::update(data_, v);
     }
 
@@ skipping 61 matching lines @@
   DISALLOW_IMPLICIT_CONSTRUCTORS(Snapshot);
 };
 
 #ifdef V8_USE_EXTERNAL_STARTUP_DATA
 void SetSnapshotFromFile(StartupData* snapshot_blob);
 #endif
 
 } }  // namespace v8::internal
 
 #endif  // V8_SNAPSHOT_SNAPSHOT_H_