Make mojo buffer allocators more robust.

mojo/public/cpp/bindings/lib/scratch_buffer.h

 // Copyright 2014 The Chromium 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 MOJO_PUBLIC_CPP_BINDINGS_LIB_SCRATCH_BUFFER_H_
 #define MOJO_PUBLIC_CPP_BINDINGS_LIB_SCRATCH_BUFFER_H_
 
 #include <deque>
 
 #include "mojo/public/cpp/bindings/buffer.h"
 #include "mojo/public/cpp/system/macros.h"
 
 namespace mojo {
 namespace internal {
 
 // The following class is designed to be allocated on the stack.  If necessary,
 // it will failover to allocating objects on the heap.
 class ScratchBuffer : public Buffer {
  public:
   ScratchBuffer();
   virtual ~ScratchBuffer();
 
   virtual void* Allocate(size_t num_bytes, Destructor func = NULL)
       MOJO_OVERRIDE;
 
  private:
-  enum { kMinSegmentSize = 512 };
+  enum {
+    kMinSegmentSize = 512,
+    kMaxSegmentSize = 1024 * 1024 * 1024,
+  };
 
   struct Segment {
     Segment* next;
     char* cursor;
     char* end;
   };
 
   void* AllocateInSegment(Segment* segment, size_t num_bytes);
-  void AddOverflowSegment(size_t delta);
+  bool AddOverflowSegment(size_t delta);
 
   char fixed_data_[kMinSegmentSize];
   Segment fixed_;
   Segment* overflow_;
 
   struct PendingDestructor {
     Destructor func;
     void* address;
   };
   std::deque<PendingDestructor> pending_dtors_;
 
   MOJO_DISALLOW_COPY_AND_ASSIGN(ScratchBuffer);
 };
 
 }  // namespace internal
 }  // namespace mojo
 
 #endif  // MOJO_PUBLIC_CPP_BINDINGS_LIB_SCRATCH_BUFFER_H_