Create and pass shared-histogram-allocator from browser to renderer.

content/common/child_process_messages.h

Index: content/common/child_process_messages.h
diff --git a/content/common/child_process_messages.h b/content/common/child_process_messages.h
index 78478cdecb9ae8c6ae15956c0d37a2036cfda447..fd5fac49351ed1859d8b71c9bc3229b4df0a6d70 100644
--- a/content/common/child_process_messages.h
+++ b/content/common/child_process_messages.h
@@ -102,8 +102,16 @@ IPC_MESSAGE_CONTROL2(ChildProcessMsg_GetChildProfilerData,
 IPC_MESSAGE_CONTROL1(ChildProcessMsg_ProfilingPhaseCompleted,
                      int /* profiling_phase */)
 
+// Sent to set the shared memory buffer to be used for storing histograms that
+// are to be reported by the browser process to UMA. The following message
+// (GetChildNonPersistentHistogramData) will return any histograms created
+// before this message is received but not any histograms created afterward.
+IPC_MESSAGE_CONTROL2(ChildProcessMsg_SetHistogramMemory,
+                     base::SharedMemoryHandle /* shm_handle */,
+                     int /* shm_size */)
+
 // Send to all the child processes to send back histogram data.
-IPC_MESSAGE_CONTROL1(ChildProcessMsg_GetChildHistogramData,
+IPC_MESSAGE_CONTROL1(ChildProcessMsg_GetChildNonPersistentHistogramData,
                      int /* sequence_number */)
 
 // Sent to child processes to tell them to enter or leave background mode.