Quick compiler: free up space in MIR.

The width field in MIR isn't especially useful - it could always
be recalculated from the Dalvik instruction.  This CL eliminates
it to allow the 16 bits it occupied to be used for the ID of the
parent BasicBlock.

Change-Id: I75ab8562ca217f0f819ecfc417014dee74bc587e
diff --git a/compiler/dex/mir_graph.h b/compiler/dex/mir_graph.h
index 11d2fbe..ded1c99 100644
--- a/compiler/dex/mir_graph.h
+++ b/compiler/dex/mir_graph.h
@@ -263,7 +263,8 @@
     Instruction::Code opcode;
   } dalvikInsn;
 
-  uint16_t width;                 // Note: width can include switch table or fill array data.
+  // TODO: Add id of parent basic block.
+  // BasicBlockId parent_bb;      // ID of parent basic block.
   NarrowDexOffset offset;         // Offset of the instruction in code units.
   uint16_t optimization_flags;
   int16_t m_unit_index;           // From which method was this MIR included