gltrace: Add support for tracing running applications.

Currently, to activate OpenGL tracing, an application has to be
start with --opengl-trace option (or have a debug prop set).

This CL adds support for tracing an application which may already
be running. This is implemented as follows:
    - DDMS initiates a JDWP message to the VM indicating that
      opengl traces be enabled.
    - When that message is received, a flag is set that indicates
      that tracing should be enabled.
    - The trace flag is checked during every eglSwap() operation,
      and if it finds that tracing should be active and it isn't,
      then it starts the tracing component.

Change-Id: I3347fe89fc06c7404d7aa9360f4b21e5bf36ebcb