Add webview tracing bit

#define ATRACE_TAG_GRAPHICS (1<<1)

#define ATRACE_TAG_INPUT    (1<<2)

#define ATRACE_TAG_VIEW     (1<<3)

#define ATRACE_TAG_LAST     ATRACE_TAG_VIEW

#define ATRACE_TAG_WEBVIEW  (1<<4)

#define ATRACE_TAG_LAST     ATRACE_TAG_WEBVIEW

#define ATRACE_TAG_VALID_MASK ((ATRACE_TAG_LAST - 1) | ATRACE_TAG_LAST)