1. A method of generating a cell library containing the layout corresponding to a plurality of cells, said method being performed within an integrated tool, said method comprising: performing placement through a placer provided in a synthesis tool if a first cell comprised in said plurality of cells is a new combinational cell, wherein a placement output is generated due to said performing placement; performing routing in said synthesis tool using said placement output to generate a routing output for said new combinational cell; performing compaction in said synthesis tool using said routing output to generate a compacted output for said new combinational cell; translating said routing output into a form suitable for providing as an input to a migration engine if said compacted output is deemed not to be of acceptable quality; providing said routing output in said form to said migration engine to generate a first layout of acceptable quality for said new combinational cell; performing layout manually if said first cell is a sequential cell to generate a second layout; providing said second layout as an input to said migration engine to perform incremental compaction; if said first cell is an existing cell and a corresponding design is to be processed uniformly, generating a target layout for said first cell using said migration engine; if said first cell is an existing cell and a corresponding design does not lend to uniform processing to generate a corresponding target layout, generating a device table indicating old parameters and corresponding new parameters, wherein said old parameters correspond to said existing cell and said new parameters correspond to said target layout; and providing said device table and said corresponding design as inputs to said migration engine to cause said target layout to be generated for said existing cell, whereby said integrated tool can be used to generate said cell library using synthesis, migration and manual approaches.